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/bin/.apm/skills/zoom-out/SKILL.md

@@ -2,6 +2,8 @@
 name: zoom-out
 description: Tell the agent to zoom out and give broader context or a higher-level perspective. Use when you're unfamiliar with a section of code or need to understand how it fits into the bigger picture.
 disable-model-invocation: true
+metadata:
+  version: "1.0.0"
 ---
 
 I don't know this area of code well. Go up a layer of abstraction. Give me a map of all the relevant modules and callers, using the project's domain glossary vocabulary.