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-submodules/references/README.md

@@ -0,0 +1,15 @@
+---
+metadata:
+  source_keys:
+    - git-scm-submodule-docs
+---
+
+# References
+
+## submodules.md
+
+Deep-dive reference: full `update` flag table, workflow patterns (clone, add, keep-pinned, update-to-latest, override URL), the complete safe-removal sequence, `absorbgitdirs`, and `foreach` shell variables. Load when SKILL.md's condensed Operations list isn't enough detail.
+
+## sources.md
+
+Research sources that informed this skill — provenance chain for git-scm-submodule-docs reference material.

plugins/git/skills/git-submodules/references/sources.md

@@ -0,0 +1,29 @@
+---
+topic: submodules
+source_keys:
+  - git-scm-submodule-docs
+---
+
+## git-scm-submodule-docs
+
+**Description:** Official git-scm.com reference for `git submodule` — all subcommands, flags, configuration keys, and behaviour details.
+
+**Source:** https://git-scm.com/docs/git-submodule
+
+- **Research doc:** plugins/git/docs/research/docs/git/submodules.md (whole-document reference — the research doc is organized by descriptive prose headings such as "Concept Overview" and "Key Commands" rather than a heading matching this slug; this key covers the entire doc, not a single section)
+
+**Contributing files:**
+- SKILL.md (all sections)
+- references/submodules.md (all sections)
+
+---
+
+Other source keys extracted during the git plugin research phase inform sibling skills in the git workflow suite, not this one:
+
+- `context7-git-htmldocs` — git:branches, git:history, git:remotes
+- `git-scm-docs` — git:configuration
+- `git-scm-worktree-docs` — git:worktrees
+- `nvie-gitflow-post`, `atlassian-gitflow-tutorial`, `gitflow-cheatsheet` — git:branches
+- `conventional-commits-spec`, `commitlint-config-conventional` — git:commits
+- `git-scm-push-docs`, `git-scm-fetch-docs`, `git-scm-pull-docs`, `git-scm-remote-docs` — git:remotes
+- `git-scm-bisect-docs`, `git-scm-log-docs`, `git-scm-diff-docs` — git:history

plugins/git/skills/git-submodules/references/submodules.md

@@ -0,0 +1,93 @@
+---
+topic: submodules
+source_keys:
+  - git-scm-submodule-docs
+---
+
+# Submodules — Deep Reference
+
+## Update flag reference
+
+| Flag | Meaning |
+|---|---|
+| `--init` | Run init first (avoids a separate step) |
+| `--remote` | Use the submodule's remote branch tip instead of the superproject's recorded commit |
+| `--checkout` | Detached HEAD at recorded commit (default) |
+| `--rebase` | Rebase current branch onto recorded commit |
+| `--merge` | Merge recorded commit into current branch |
+| `--recursive` | Operate on nested submodules |
+| `--jobs <n>` | Parallel clone (defaults to `submodule.fetchJobs`) |
+| `-N` / `--no-fetch` | Skip remote fetch |
+| `--depth <n>` | Shallow clone |
+| `--filter <spec>` | Partial clone filter |
+
+## Workflow patterns
+
+### Clone a repo with submodules
+```bash
+git clone --recurse-submodules <url>   # Git 2.13+, one step
+# or
+git clone <url>
+git submodule update --init --recursive
+```
+
+### Add a dependency as a submodule
+```bash
+git submodule add https://github.com/org/lib.git libs/lib
+git commit -m "chore: add lib as submodule"
+```
+
+### Keep submodules pinned to the superproject's recorded commit
+```bash
+git submodule update --recursive   # after every git pull
+git config submodule.recurse true  # do this automatically on pull
+```
+
+### Update submodules to the latest commit on their tracked branch
+```bash
+git submodule update --remote --merge --recursive
+git commit -am "chore: update submodules to latest"
+```
+
+### Override a submodule URL locally (private mirror)
+```bash
+git submodule init
+# edit .git/config: submodule.<name>.url = <mirror-url>
+git submodule update
+```
+Local-only override (`.git/config`, not `.gitmodules`) — doesn't propagate to collaborators. Re-running `sync` overwrites it with the `.gitmodules` URL.
+
+## Removal, in full
+
+`deinit` alone does not remove a submodule — it only clears `.git/config` and empties the working tree. To fully remove:
+```bash
+git submodule deinit -f <path>   # unregister from .git/config
+git rm <path>                     # remove .gitmodules entry + gitlink from index
+rm -rf .git/modules/<name>/       # stale git dir; not tracked by git, not auto-cleaned
+git commit -m "chore: remove <name> submodule"
+```
+`.git/modules/<name>/` persisting after `git rm` will block re-adding the same path until manually deleted.
+
+## Relocate an embedded `.git` directory
+
+```bash
+git submodule absorbgitdirs [<path>...]
+```
+Moves a submodule's own `.git` directory into the superproject's `.git/modules/<name>/`, linking it back with a `.git` pointer file. Needed when a submodule was created or copied without going through `git submodule add` (e.g. converting a plain nested repo into a proper submodule).
+
+## `foreach` shell variables
+
+Available inside the `<command>` argument to `git submodule foreach`:
+
+| Variable | Meaning |
+|---|---|
+| `$name` | Logical submodule name |
+| `$sm_path` | Path relative to superproject root |
+| `$displaypath` | Path relative to current working directory |
+| `$sha1` | Recorded commit SHA |
+| `$toplevel` | Superproject's root path |
+
+```bash
+git submodule foreach --recursive '<command>'
+git submodule foreach 'git pull origin main || :'   # || : continues past failures
+```