Slice 9: git_checkout and create_branch (menu + MCP)

git boundary Checkout/CreateBranch; service GitCheckout/GitCreateBranch (activity detail names the branch; gitAction takes an ok-detail). HTTP /api/repo/git ops checkout + create-branch (branch field). MCP tools git_checkout and create_branch. <repo-menu> gains Switch branch… and New branch… (prompt for name). Service test covers create+switch and existing-branch failure. Checkout is not destructive - git refuses if it would overwrite changes.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

components/repo-menu/repo-menu.md

@@ -11,10 +11,11 @@ event. Safe commands run on click; the destructive one confirms first (§1.4).
 - **Listens:** `repo:contextmenu` on `document` — `detail: { repo, x, y }`
   (dispatched by `<repo-list>` on right-click). Shows the menu at (x, y).
 - **Commands → endpoints:**
-  - Get latest / Publish / Check for updates / Save my work… / Discard all
-    changes… → `POST /api/repo/git {path, op, message?}` (op: pull/push/fetch/
-    commit/discard). "Save my work…" prompts for a message; "Discard all
-    changes…" confirms (destructive).
+  - Get latest / Publish / Check for updates / Save my work… / Switch branch… /
+    New branch… / Discard all changes… → `POST /api/repo/git {path, op,
+    message?, branch?}` (op: pull/push/fetch/commit/checkout/create-branch/
+    discard). "Save my work…" prompts for a message; "Switch branch…"/"New
+    branch…" prompt for the branch; "Discard all changes…" confirms (destructive).
   - Set as active project → `POST /api/active-project`.
   - Ask Claude to switch here → `POST /api/switch` (the handoff request).
   - Copy path → clipboard.
@@ -23,6 +24,8 @@ event. Safe commands run on click; the destructive one confirms first (§1.4).
 ## History
 - 2026-09-20: created — slice 6; plain-language git commands + coordination
   actions, backed by the shared service layer (same ops Claude gets via MCP).
+- 2026-09-20: added "Switch branch…" (checkout) and "New branch…" (create-branch),
+  both prompting for the branch name (slice 9).
 
 ## Notes / gotchas
 - Results aren't shown inline; they appear in `<activity-feed>` (each op records a