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-history/README.md

@@ -0,0 +1,24 @@
+# git-history
+
+Inspect git history — log queries, bisect, and locating problematic commits.
+
+## What it does
+
+This skill handles history inspection within the git workflow suite. It queries logs with pickaxe/line-range/custom formats, runs bisect to find bug-introducing commits, and locates commits for downstream cherry-picking or reverting. It returns structured results for agent composition. Rebase, squash, fixup, and other history-rewriting operations are owned by git-commits, not this skill.
+
+## Usage
+
+```
+/git-history
+```
+
+Describe your history task: search logs, bisect for a regression, or locate a specific commit. The skill will query history and return structured results.
+
+## Files
+
+| File | Purpose |
+|------|---------|
+| `SKILL.md` | Skill instructions for agents |
+| `references/git-log-format.md` | Full log format placeholders, diff-filter letters, `-L` syntax, ancestry filters, diff output-control flags |
+| `references/sources.md` | Research sources and provenance |
+| `references/README.md` | Index of the references directory |