refactor(skills): mandate metadata.version on every skill's frontmatter

Only 12 of 39 skills carried metadata.version, and adoption tracked
which plugin a skill lived in rather than any stated rule: core,
gitea and lint were consistent adopters, bin and kyberforge were
consistent non-adopters, git was split with one outlier. There was
no documented convention, and skill-author's own bump logic was
already written as if presence were conditional.

metadata.version is now required on every skill. The 19 skills here
that never carried one (bin, kyberforge, gitea-files) are seeded at
1.0.0, not 0.1.0 -- that value stays reserved for a skill's actual
creation point under skill-author's existing convention. The
skill-frontmatter pre-commit hook now fails a SKILL.md missing the
field, the same class of failure as a missing name/description.

Full rationale in the new ADR. The git-plugin skills that also need
this field follow in the next commit, bundled with issue #113's rtk
normalization since both touch the same files.

Refs: #127
ADR: 0022
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EeH8SCbcrCAQrtymkNuhKP

docs/adr/0022-skill-metadata-version-is-mandatory.md

@@ -0,0 +1,70 @@
+# Every skill's `metadata.version` is mandatory, not a per-plugin option
+
+**Status: accepted (2026-09-07).**
+
+## Context
+
+`metadata.version` is optional SKILL.md frontmatter (`create.md`'s "Optional frontmatter" list:
+"uncomment and fill in, or remove entirely"). `skill-author`'s own bump logic was written
+conditionally — "with `metadata.version` present, bump the minor version on create... and the
+patch version on improve" — which only makes sense if presence is a real per-skill choice.
+
+Adoption never followed a rule; it followed the plugin. Of 39 skills, 12 carry a version:
+
+| Plugin | Has it | Total |
+|---|---|---|
+| `core` | 3 | 3 |
+| `gitea` | 6 | 7 |
+| `lint` | 2 | 2 |
+| `git` | 1 | 9 |
+| `bin` | 0 | 11 |
+| `kyberforge` | 0 | 7 |
+
+`core`, `gitea` and `lint` are consistent adopters (`gitea-files` the one gap); `bin` and
+`kyberforge` are consistent non-adopters; `git` has one outlier (`git-commits`, versioned for no
+plugin-specific reason found on inspection — no comment, no cross-reference, nothing distinguishing
+it from its eight siblings). Issue #127 raised this as an undocumented split: two house norms
+coexisting with no stated rule for which applies where, the same class of defect as an unstated
+`rtk`/bare-`git` convention (#113) found in the same audit pass.
+
+## Decision
+
+**Every skill's frontmatter carries `metadata.version`.** It is no longer optional, and no longer a
+per-plugin choice.
+
+- **The 27 skills that never carried one are seeded at `1.0.0`**, not `0.1.0`. `0.1.0` is
+  `skill-author`'s existing new-skill starting point, chosen for a skill with no revision history to
+  its name yet. These 27 have all been through the ADR-0020 retrofit and repeated audit passes
+  without ever tracking a version; crediting them with `0.1.0` would understate that, and there is
+  no real history to justify seeding higher than a first stable release. `1.0.0` marks "versioned as
+  of this retrofit," `0.1.0` keeps meaning "created and never yet revised."
+- **New skills still start at `0.1.0`.** `skill-author`'s create/improve bump convention is
+  unchanged; only the presence of the field stops being conditional.
+- **The one outlier in the other direction, `git-commits`, keeps its existing value** (`0.1.3`) —
+  it already had real tracked history under the old conditional rule, and this decision does not
+  reset skills that were already compliant.
+- **`skill-frontmatter`'s pre-commit hook gains the check.** It already fails a SKILL.md missing
+  `name:` or `description:`; a missing `metadata.version` is now the same class of failure, not a
+  style nit an audit might or might not catch.
+
+## Considered options
+
+**Leave it per-plugin, document the split.** This was the initial framing of #127 and is coherent —
+`core`/`gitea`/`lint` keep it, `bin`/`kyberforge` don't, two outliers get normalized to match their
+plugin. Rejected on reconsideration: a rule that says "some plugins track this and some don't" is
+strictly harder to state, audit and onboard against than "every skill does," for a field whose entire
+job is answering "did this change since I last read it" — a question with the same shape everywhere
+it's asked, not one that varies by plugin domain.
+
+**Drop the field corpus-wide.** Rejected: `skill-author` already depends on it to decide whether a
+create/improve pass owes a bump, so the 12 skills carrying it are not tracking dead weight — removing
+it discards real revision signal for no gain.
+
+## Consequences
+
+27 SKILL.md files gain `metadata.version: "1.0.0"`. `skill-author`'s `create.md` moves the field from
+"Optional frontmatter" to the required list, citing this ADR. `skill-author`'s own SKILL.md drops the
+"with `metadata.version` present" conditional in its bump-rule line, since presence is no longer in
+question. `.pre-commit-config.yaml`'s `skill-frontmatter` hook is extended to require the field,
+closing the gap #113 and #118 both named in the same audit pass: a stated rule with nothing enforcing
+it drifts the same way an unstated one does.