refactor(git-branches): retrofit to the ADR-0020 context contract

Description 612 -> 273 chars, body 1124 -> 457 words. Branch patterns,
operations, merging, comparison, and the orchestrator contract move to
references/.

Corrects rebase routing in four places: this skill sent rebase to
git-history, which carries no rebase content and disclaims it. Rebase is
git-commits'; cherry-pick and revert stay git-history's. Drops a Step 3
gate on a rebase flow this skill does not have.

plugins/git/.apm/skills/git-branches/references/branch-operations.md

@@ -0,0 +1,34 @@
+---
+source_keys:
+  - context7-git-htmldocs
+---
+
+# Per-action command mapping
+
+One command per action. Where two forms exist, the first is the default and the second the escape
+hatch.
+
+- **create** — `git switch -c <branch> <base>`. Base comes from the config's `base_branch`
+  (`main` under GitHub Flow, usually `develop` under Gitflow).
+- **switch** — `git switch <branch>` moves to an existing local branch; it aborts rather than
+  clobbering conflicting local changes. `git switch -` returns to the previous branch.
+- **delete (local)** — `git branch -d <branch>` refuses when the branch holds unmerged commits,
+  which is why it is the default. `git branch -D <branch>` forces the deletion and discards that
+  work — only after the destructive-operation gates pass and `confirm: true` is set.
+- **delete (remote)** — `git push origin --delete <branch>`.
+- **rename** — `git branch -m <old> <new>`.
+- **list** — `git branch` (local), `-a` (local plus remote-tracking), `-r` (remote-tracking only),
+  `--merged` / `--no-merged` (filter by merge status into the current branch).
+- **track** — `git branch --set-upstream-to=origin/<branch>` sets an upstream without pushing.
+  `git branch -vv` shows the tracking state of every local branch.
+
+## get-intent
+
+Git has no native field for free-text branch metadata, and this skill does not persist any. On
+`create`, the `intent` value is only returned in the structured result — the caller decides
+whether to store it.
+
+On `get-intent`, either parse the intent back out of the branch-name convention
+(`feature/<intent-slug>`) or return `{ "intent": null }` when the caller never persisted the
+create-time value. Never fabricate an intent: a downstream commit message built on a guessed
+intent is worse than one built on none.

plugins/git/.apm/skills/git-branches/references/branch-patterns.md

@@ -0,0 +1,31 @@
+---
+source_keys:
+  - nvie-gitflow-post
+  - atlassian-gitflow-tutorial
+  - gitflow-cheatsheet
+---
+
+# Branch patterns
+
+Which pattern is in play decides the base branch, the branch name prefix, and whether merges are
+allowed to fast-forward. Default to GitHub Flow — simpler, and what CI/CD-oriented repos expect.
+Fall back to Gitflow only when the config says so or the repo already carries `develop` or
+`release/*` branches.
+
+## GitHub Flow
+
+- Base: `main`
+- Feature branches: `feature/<feature-name>` or `fix/<bug-name>`
+- Merge: fast-forward where possible, to keep history linear
+- Delete the branch after merge
+
+## Gitflow
+
+- Base: `main` (production) plus `develop` (integration)
+- Feature branches: `feature/<feature-name>`, cut from `develop`
+- Release branches: `release/X.Y.Z`, cut from `develop`, merged to both `main` and `develop`
+- Hotfix branches: `hotfix/X.Y.Z`, cut from `main`, merged to both `main` and `develop`
+- Merge: always `--no-ff`, so the branch structure survives in the history
+
+The two are not mixable. A `--no-ff` merge into a GitHub Flow repo leaves merge commits nobody
+expects; a fast-forward merge of a Gitflow release branch erases the release boundary.

plugins/git/.apm/skills/git-branches/references/comparing-branches.md

@@ -0,0 +1,16 @@
+---
+source_keys:
+  - context7-git-htmldocs
+---
+
+# Comparing two branches
+
+The two-dot and three-dot forms mean different things and are easy to swap by accident — check the
+direction before reporting a result.
+
+- `git log main..feature` — commits on `feature` that are not on `main`.
+- `git log feature..main` — the reverse direction: commits on `main` not on `feature`.
+- `git log --left-right main...feature` — both diverging sets at once (symmetric difference).
+- `git diff main...feature` — the diff from the common ancestor to `feature`'s tip, which is what
+  a reviewer sees, rather than the diff between the two tips.
+- `git merge-base main feature` — print the common ancestor commit.

plugins/git/.apm/skills/git-branches/references/merging.md

@@ -0,0 +1,29 @@
+---
+source_keys:
+  - context7-git-htmldocs
+---
+
+# Merging one branch into another
+
+Scope is fast-forward and merge-commit mechanics plus conflict resolution. Rebase belongs to
+`git-commits`; cherry-pick and revert to `git-history`.
+
+- **Fast-forward** — `git merge <branch>` advances the pointer with no merge commit when the
+  target has not diverged.
+- **True merge** — `git merge --no-ff <branch>` forces a merge commit even when a fast-forward is
+  possible. Gitflow requires it on every supporting-branch merge.
+- **Squash merge** — `git merge --squash <branch>` stages the combined diff without committing.
+  Follow it with a `git commit`.
+- **Octopus merge** — `git merge branch-a branch-b branch-c` merges more than two branches at
+  once, but fails outright on any conflict. Use sequential two-way merges when conflicts are
+  likely.
+
+## Conflict resolution
+
+When Git cannot auto-merge it writes conflict markers and stops mid-merge. Run `git status` to
+list the conflicted files, edit each to resolve its markers, then `git add <file>` and
+`git merge --continue`.
+
+- `git merge --abort` restores the pre-merge state.
+- `git mergetool` opens the configured merge tool.
+- `git diff --diff-filter=U` shows only the still-conflicted files.

plugins/git/.apm/skills/git-branches/references/orchestrator-contract.md

@@ -0,0 +1,16 @@
+# Orchestrator request contract
+
+`git-orchestrate` and other calling agents send this shape. The result shape they parse back is in
+`SKILL.md` Step 5, because every run emits one.
+
+Request:
+
+```json
+{
+  "action": "create|switch|delete|rename|track|list|get-intent",
+  "branch": "<branch-name>",
+  "base": "<base branch, optional, defaults to config>",
+  "intent": "<human-readable intent, optional>",
+  "confirm": "<true for destructive ops, omit for read ops>"
+}
+```

plugins/git/.apm/skills/git-branches/references/sources.md

@@ -12,7 +12,8 @@
 - **Research doc:** plugins/git/docs/research/docs/git/gitflow.md (whole-document reference)
 
 **Contributing files:**
-- SKILL.md (Branch Patterns — Gitflow vs. GitHub Flow structure and defaults)
+- SKILL.md (Gitflow vs. GitHub Flow inference and the not-mixable rule)
+- references/branch-patterns.md (Gitflow vs. GitHub Flow structure, defaults, and why the two are not mixable)
 
 ## atlassian-gitflow-tutorial
 
@@ -23,7 +24,9 @@
 - **Research doc:** plugins/git/docs/research/docs/git/gitflow.md (whole-document reference)
 
 **Contributing files:**
-- SKILL.md (Branch Patterns — Gitflow branch types, base/merge targets, `--no-ff` requirement)
+- SKILL.md (Gitflow vs. GitHub Flow inference and the not-mixable rule)
+- references/branch-patterns.md (Gitflow branch types, base/merge targets, `--no-ff` requirement)
+- references/merging.md (`--no-ff` requirement on Gitflow supporting-branch merges)
 
 ## gitflow-cheatsheet
 
@@ -34,7 +37,7 @@
 - **Research doc:** plugins/git/docs/research/docs/git/gitflow.md (whole-document reference)
 
 **Contributing files:**
-- SKILL.md (Branch Patterns — feature/release/hotfix naming conventions)
+- references/branch-patterns.md (feature/release/hotfix naming conventions)
 
 ## context7-git-htmldocs
 
@@ -45,4 +48,7 @@
 - **Research doc:** plugins/git/docs/research/docs/git/branching-merging.md (whole-document reference)
 
 **Contributing files:**
-- SKILL.md (Command mapping, Merging, Comparing Branches — `git switch`/`git branch`/`git merge`/`git log`/`git diff`/`git merge-base` command vocabulary and flags)
+- SKILL.md (Gotchas — `git switch` abort-on-conflict behaviour, branch/tag name ambiguity)
+- references/branch-operations.md (`git switch`/`git branch` command vocabulary and flags)
+- references/merging.md (`git merge` strategies and conflict-resolution commands)
+- references/comparing-branches.md (`git log`/`git diff`/`git merge-base` range syntax)