refactor(git): normalize rtk-prefix usage, add metadata.version

Two bundled fixes across the same nine skills, since both touch the
same files.

Issue #113: skill prose used rtk git and bare git inconsistently for
the same operations, with no stated rule for which applied where.
Executable instructed commands (a dispatch-table "Run" cell, a fenced
code-block procedure, an imperative step) now consistently use rtk
git; illustrative or referential mentions -- naming a flag's behavior,
quoting a doc heading, warning against an anti-pattern -- stay bare
git. Documented in the new plugins/git/README.md, scoped to this
plugin only: gitea-* skills talk to the server over MCP tools and
carry no git/rtk mentions at all.

Also the git-plugin slice of #127: metadata.version added to the
eight skills that lacked it. git-commits already had one and is
untouched.

Fixes: #113
Fixes: #127
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EeH8SCbcrCAQrtymkNuhKP

plugins/git/.apm/skills/pc-run/references/failure-patterns.md

@@ -14,8 +14,8 @@ Cause: A fixer hook (e.g. `trailing-whitespace`, `end-of-file-fixer`, `pretty-fo
 
 Fix: Re-stage and recommit.
 ```bash
-git add -u
-git commit -m "same message"
+rtk git add -u
+rtk git commit -m "same message"
 ```
 
 Do NOT reach for `pre-commit install -f` here. That flag overwrites existing hook files in `.git/hooks/`; it has nothing to do with re-staging.