feat(git-plugin): add complete git workflow automation suite

## Why
The git plugin only covered a partial slice of common git workflows.
This adds the remaining skill set (branches, commits, history, remotes,
submodules, workflow, worktrees) plus a git-orchestrate agent so the
plugin can handle end-to-end git automation instead of a handful of
commands.

## Implementation Notes
Each new skill was validated against its research docs and org
conventions after initial authoring, which surfaced hallucinated
version pins, factual errors, and completeness gaps that were
corrected in the same pass rather than left for follow-up.

## Impact
Bumps the git plugin to 1.3.0.

Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>

plugins/git/skills/git-commits/README.md

@@ -0,0 +1,24 @@
+# git-commits
+
+Create, amend, squash, and cherry-pick commits with Conventional Commits formatting and validation.
+
+## What it does
+
+This skill handles commit operations within the git workflow suite. It generates well-formatted commit messages following the Conventional Commits spec, validates against commitlint config-conventional constraints, and communicates SemVer impact. It enforces confirmation gates for history-altering operations (amend, rebase, squash) and returns structured JSON output for agent consumption.
+
+## Usage
+
+```
+/git-commits
+```
+
+Describe your commit task: create a new commit, amend, squash, or cherry-pick. The skill will guide message formatting and handle confirmation for destructive operations.
+
+## Files
+
+| File | Purpose |
+|------|---------|
+| `SKILL.md` | Skill instructions for agents |
+| `references/conventional-commits-spec.md` | Full Conventional Commits specification |
+| `references/commit-template.md` | Why / Implementation Notes / Impact body structure and full trailer list |
+| `references/sources.md` | Research sources and provenance |