fix(kyberforge): announce every provenance skip and scope checks 7-8 to source indexes

The clean provenance bill was an artifact. Checks 7 and 8 assume `Research doc:`
names a source index whose H2s are slugs, but 30 of 121 corpus entries point at
topic content documents whose H2s are topics. Those 30 produced every new check-7
INFO — all false positives. Check 8 aimed at the same documents, which carry no
`Status:` line at all, would have emitted a large false-FAIL flood; the only thing
preventing it was an unannounced `rd_status != extracted` skip. So "0 new FAILs"
rested on exactly the fail-open class this branch exists to remove, and naively
fixing the skip would have turned the branch red.

Checks 7/8 now run only when the research doc's basename is `sources.md`, and every
other case emits a visible INFO naming the slug. The dangling-path INFO stays ahead
of the basename gate, because a path that does not resolve is rot whatever it is
named. `parse_status` accepts the bullet form and a trailing note after the
backticked value, so a status it cannot read no longer reads as "nothing to check".

Corpus: 36 INFOs of which 30 were false, to 56 of which none are. FAIL stays 0, and
no Status line flipped to `extracted` under the new parser, so no FAIL was
suppressed by luck.

Also closed, each a silent pass: a nonexistent directory, a directory with no
SKILL.md, and extra arguments now exit 2; a UTF-8 BOM no longer defeats frontmatter
parsing; the bare `except Exception: return False` that turned an unreadable file
into a clean pass is gone, with all reads pinned to UTF-8; check 3 walks nested
`references/` subdirectories; `FILL IN:` at end of line no longer escapes checks 1
and 6; duplicate `## slug` blocks and repeated `Research doc:` lines are announced
rather than half-read.

The agent-audit copy carried all of the above unfixed and is now ported, minus the
four fixes that are genuinely N/A at agent scope — it reads a plugin-root
`sources.md` and has no checks 7/8 and no `references/` tree. Its silent exit 0 for
a file outside plugin scope is preserved deliberately: that is a verdict about a
valid file, not a skip, and `check-scope-walkup-sync.sh` pins it. Every exit-2 gate
therefore decides from the argument alone, before the walk-up runs.

`validation-scripts.md` said flatly that silence from the validator is a pass, not
a skip. That sentence is what made a typo'd path dangerous, and both copies are
corrected here. The matching SKILL.md exit-code guidance lands with the audit
rubric change, which touches the same files.

Tests: skill-audit 45 to 65, agent-audit 24 to 43, every new case proven by mutation.

Refs: #111, #118, #121

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

@@ -34,8 +34,14 @@ first of these:
 `plugin.json` and no `apm.yml` falls through to project or user scope.
 
 `validate-provenance.sh` exits 0 silently when that walk does not land on a package root, and again
-when the package has no provenance data. Silence from it is a pass, not a skip you need to
-investigate.
+when the package has no provenance data. Check the exit code before you believe the silence:
+
+- **0** — a pass, not a skip you need to investigate. Both silent cases above land here.
+- **1** — real findings, on stdout with Why and Fix.
+- **2** — the check never ran. A missing, doubled, non-file or wrongly-named argument, an
+  undecodable `apm.yml`, or an absent `python3`, each with a diagnostic on stderr and no findings
+  at all. Report the `### Provenance` dimension as unverified and quote the reason. An exit 2 is
+  never a clean pass: empty stdout there means nothing was checked, not that nothing was wrong.
 
 ## Manual fallback