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/git-submodules/SKILL.md

@@ -9,6 +9,7 @@ description: >
   Not the superproject's own remotes -> `git-remotes`.
 
 metadata:
+  version: "1.0.0"
   category: git
   source_keys:
     - git-scm-submodule-docs