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-workflow/references/sources.md

@@ -0,0 +1,59 @@
+---
+# Research sources referenced by this skill
+# Each entry documents where the skill's guidance came from.
+---
+
+## nvie-gitflow-post
+
+**Description:** Original 2010 post by Vincent Driessen introducing the Gitflow branching model, including a 2020 reflection note recommending GitHub Flow for continuous delivery teams.
+
+**Source:** https://nvie.com/posts/a-successful-git-branching-model/
+
+- **Research doc:** plugins/git/docs/research/docs/git/gitflow.md (whole-document reference)
+
+**Contributing files:**
+- SKILL.md (Interaction style — branching-model-aware tips)
+
+## atlassian-gitflow-tutorial
+
+**Description:** Atlassian's comprehensive Gitflow tutorial covering all five branch types, lifecycle steps, and CLI usage.
+
+**Source:** https://www.atlassian.com/git/tutorials/comparing-workflows/gitflow-workflow
+
+- **Research doc:** plugins/git/docs/research/docs/git/gitflow.md (whole-document reference)
+
+**Contributing files:**
+- SKILL.md (Interaction style — branching-model-aware tips)
+
+## gitflow-cheatsheet
+
+**Description:** Visual cheatsheet for the git-flow CLI commands (git-flow-avh fork), covering all subcommands for feature, release, and hotfix branches.
+
+**Source:** https://danielkummer.github.io/git-flow-cheatsheet/
+
+- **Research doc:** plugins/git/docs/research/docs/git/gitflow.md (whole-document reference)
+
+**Contributing files:**
+- SKILL.md (Interaction style — branching-model-aware tips)
+
+## context7-git-htmldocs
+
+**Description:** Official Git HTML documentation from the git/htmldocs repository — covers all commands, concepts, and internals.
+
+**Source:** context7:/git/htmldocs
+
+- **Research doc:** plugins/git/docs/research/docs/git/overview.md (whole-document reference)
+
+**Contributing files:**
+- SKILL.md (Workflow — general git operation vocabulary)
+
+## org-git-conventions
+
+**Description:** This org's internal git conventions (hard rules on hooks, force-push, atomic commits, secrets, Conventional Commits, trailers, and the `rtk git` wrapper requirement). Originally maintained as a standalone instruction file loaded into every agent's context; embedded directly into this skill because that central file has been removed from the repo, and skill content must stay self-contained after plugin installation.
+
+**Source:** org-internal (formerly `core/instructions/git.md` in this repo, prior to its removal)
+
+- **Research doc:** none — org convention, not part of the plugin's research corpus (no `plugins/git/docs/research/` topic file backs this entry)
+
+**Contributing files:**
+- SKILL.md (Gotchas — Hard rules subsection, rtk git note)