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

plugins/gitea/.apm/skills/gitea-files/SKILL.md

@@ -11,6 +11,7 @@ compatibility: Requires the Gitea MCP server configured with a token scoped to a
   is not actually required for any of this domain's five tools.
 
 metadata:
+  version: "1.0.0"
   category: gitea
   source_keys:
     - gitea-mcp-repo