fix(kyberforge): restore skill-audit's script-failure fallback and E100 diagnostic

The ADR-0020 body trim took `skill-audit` from 2,623 body words to a dispatch
shape, and two things went out with it that were not padding.

The manual structural fallback was one. Its replacement was a single sentence
telling the auditor to report an INFO when `validate.sh` cannot run — so with no
`python3` or no PyYAML, `skill-audit` reported the gap honestly and then audited
nothing structural at all. Every ADR-0020 measurement, the whole-file ceilings,
the name-to-directory match, the `references/` pointer check and the script
hygiene checks silently left the audit. A skill's whole Structure dimension
hanging on one optional interpreter is the same vacuous-pass shape the gate
scripts were just fixed for, one layer up.

The `E100 Runtime error ... does not exist` diagnostic was the other. That exit
code means an explicit relative `--config` was passed to `vale-wrap.sh` while
vale itself was installed and working; without the note, Step 1's fallback reads
exit 2 as "vale unavailable" and downgrades the description, body-discipline and
patterns dimensions to full LLM judgment for a config error it could have fixed.
That misreading is already recorded in CONTEXT.md as the reason both audit skills
stopped passing `--config` at all.

Both are restored in `references/validation-scripts.md`, loaded only when a Step 1
script fails — so the body pays nothing for them on a clean run, which is what the
dispatch pattern is for. The file also carries the by-hand boundary-target
procedure and the three ways to misread the result, including that
`INFO ... DID NOT RUN` is not a pass.

`references/file-structure.md` gains the one sanctioned spelling for a cross-skill
reference. The possessive form (``skill-audit's references/validation-scripts.md``)
is the only spelling both rules accept: a full repo path is what that section
already forbids, and a bare `references/<file>.md` is now a hard ERROR from the
ADR-0020 pointer check, which requires the file to exist in the skill's *own*
directory. Without the rule the two constraints look mutually exclusive.

Refs: ADR-0020

plugins/kyberforge/skills/skill-audit/references/validation-scripts.md

@@ -0,0 +1,118 @@
+---
+source_keys:
+  - agentskills-spec
+  - agentskills-using-scripts
+---
+
+# Validation Scripts Reference
+
+Read this when a Step 1 script fails, cannot run, or reports something that needs interpreting.
+Nothing here is needed on a clean run.
+
+## Report the gap, do not guess
+
+If a script cannot run at all — Bash denied, `python3` unavailable, PyYAML not importable, `vale`
+not installed — say so as an **INFO** finding naming the script and the missing dependency, then
+fall back to the manual checks below. An INFO never changes PASS/FAIL. Silently omitting the
+dimension a script would have covered reports a clean audit that checked less than it claims to
+have checked, and the Step 4 coverage line then names a dimension nothing actually examined.
+
+## Manual structural fallback
+
+`validate.sh` needs `python3` **and** PyYAML, and refuses to start without either — the description
+value has to be measured after YAML folding is resolved, so skipping the ADR-0020 gates would be a
+vacuous pass rather than a partial one. The two are checked separately, so the message already names
+the right one — report it verbatim rather than diagnosing further:
+
+```text
+Error: python3 is required but was not found on PATH.
+Error: PyYAML is required but is not importable by python3.
+```
+
+Without them — or with Bash denied, or on a permission error — work this list
+by hand and file the results under `### Structure` exactly as the script's output would have been:
+
+- **`name`** present, 1–64 characters, kebab-case (lowercase letters, digits and hyphens; no
+  leading, trailing or doubled hyphen), and **matching the skill's directory name** exactly.
+- **`description`** present and non-empty; no unfilled `FILL IN:` placeholder in it. An absent or
+  empty description is a **FAIL**, never a silent skip — it is the one field preloaded into every
+  session, so a skill without one can never be routed to.
+- **Description length**, measured on the folded YAML value with newlines collapsed to single
+  spaces — not on the raw block scalar, which counts indentation. 250 characters SUGGESTION, 400
+  FAIL (ADR-0020), 1,024 FAIL (agentskills.io spec).
+- **Body length**, counting everything after the frontmatter's closing `---`. 600 words
+  SUGGESTION, 900 FAIL (ADR-0020).
+- **Whole-file ceilings**, counting the file including frontmatter: 500 lines FAIL, 2,770 words
+  FAIL (agentskills.io spec). These are a different measurement from the two above — report them
+  as separate findings, never merged.
+- **A boundary clause is present** — either the prose form (`do not` / `instead` / `rather than` /
+  `not for`) or ADR-0020's compressed `Not <thing> -> <name>` arrow. **SUGGESTION**, not FAIL:
+  the absence is deterministic, but whether this skill warrants one is the auditor's call.
+- **Boundary targets resolve** — **FAIL** on a name that resolves to nothing. See the section
+  below; resolving these by hand is the one item on this list with a procedure of its own.
+- **Every `references/<file>.md` named in the body exists on disk** — **FAIL**, not a suggestion.
+  A dispatch table or "read X" trigger naming a missing file sends the agent nowhere. Ignore
+  mentions inside fenced code blocks, and ignore a mention whose own line says the file is gone
+  (`removed`, `deleted`, `renamed`, `superseded`, `replaced`, `obsolete`, `deprecated`, `former`,
+  `gone`, `no longer`, `used to`) — that is a historical note, not a dispatch entry.
+- **Gotchas discipline**, both **SUGGESTION**. Locate the section by a heading that *is* Gotchas
+  (`## Common Gotchas` counts; `## Gotcha handling` and `## Why gotchas matter` do not), running to
+  the next heading at the same level or shallower. More than five top-level entries is one
+  suggestion; a section over 25% of the body word count is a second, independent one. Count
+  entries at column 0 only — an indented child bullet is not an entry — and ignore fenced code
+  blocks for both.
+- **No unfilled `FILL IN:` placeholder** anywhere in the body.
+- **Every file in `scripts/`** carries the executable bit and contains no interactive prompt —
+  no bare `read`, no `select`, nothing that blocks on a TTY.
+
+## Resolving boundary targets by hand
+
+Targets are read from **both** boundary forms. The compressed `Not <thing> -> <name>` arrow and the
+prose form are each parsed *and* target-checked, so a typo in prose phrasing fails exactly as an
+arrow typo does — do not check only the names after an arrow.
+
+Build the universe by walking up **from the `SKILL.md` under audit**, never from the validator's own
+location. The nearest ancestor holding `plugins/*/.apm/skills/` or `plugins/*/.apm/agents/` is the
+authoring root, falling back to the nearest ancestor holding `.git`. When one is found the universe
+is every skill and agent under `<root>/plugins/*/`, plus the skill's own apm package, plus the
+packages that package declares in its `apm.yml` under `dependencies.apm`. Deployed `.claude/` and
+`.agents/` trees are consulted **only** when no authoring root exists — they are gitignored
+`apm install` output, and reading them would make a fresh clone and a developer machine disagree.
+
+Three ways to read the result wrong:
+
+- **A hyphenated name used attributively is not a dangling target.** "Use pre-commit hooks instead
+  of ad-hoc scripts" reads as a route to `pre-commit` on wording alone. What separates a route from
+  prose is grammar: a route target is terminal — followed by punctuation, a conjunction, or a
+  boundary word — whereas a compound modifier is followed by the noun it modifies. A name followed
+  by an ordinary noun still *confirms* a route when it exists, but never raises a FAIL on its own.
+- **A SUGGESTION-tier unresolved target is not a FAIL you may promote.** Terminal position alone is
+  not evidence of a route: "run `pre-commit` instead", "see `commit-msg`" and "use the clean-up
+  instead" are all terminal and all prose. A prose-form target earns a FAIL only when its own
+  sentence names another target that *does* resolve; otherwise the script reports it and moves on,
+  and so should you. Route notation — `/name` and `-> name` — is exempt and always FAILs, and it is
+  the fix to recommend when the author did mean a route.
+- **`INFO boundary-target resolution DID NOT RUN` is not a pass.** The script prints it, and exits
+  0, when no universe could be determined for that path — the usual cause being a skill copy
+  audited outside its package. Report it as an INFO naming the unchecked targets and re-run against
+  the real directory; filing it as clean signs off targets nothing verified.
+
+## Script-specific failures
+
+- **`validate-provenance.sh` printed nothing.** That is a pass, not a skip. It also exits 0
+  silently when the skill has no `source_keys` and no `references/sources.md` — nothing to
+  validate is not a finding.
+- **`vale` reports `0 files`.** Treat the pass as NOT RUN, not as clean, and fall back to full
+  Step 3 judgment for the dimensions it would have covered. The bundled `Kyberforge` style is
+  scoped by glob in `assets/vale/.vale.ini`; a file outside those globs is silently not linted.
+- **`E100 Runtime error ... does not exist` (exit 2) from `vale-wrap.sh`.** An explicit relative
+  `--config` was passed. Pass none: the wrapper locates its own `assets/vale/.vale.ini` from its
+  own path, so a resolved script path plus an unresolved config path produces exactly this. Do not
+  read this exit code as vale being unavailable — that misreading sends the audit down the
+  fallback path while vale was installed and working the whole time.
+- **The `vale` binary is genuinely absent** (`command not found`). Report one INFO naming it, then
+  fall back to full Step 3 judgment for the description, body-discipline and patterns dimensions —
+  the prefilter's whole coverage. Judge those by rubric rather than dropping them.
+- **A path argument that does not exist is a hard error** in `vale-wrap.sh`, deliberately: bare
+  `vale` would fall back to reading stdin and print a clean-looking `0 errors ... in stdin`, which
+  the `0 files` guard above does not catch.