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>

cmd/server/main.go

@@ -195,6 +195,7 @@ func main() {
 			Path    string `json:"path"`
 			Op      string `json:"op"`
 			Message string `json:"message"`
+			Branch  string `json:"branch"`
 		}
 		if err := c.Bind(&body); err != nil {
 			return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid body"})
@@ -213,6 +214,10 @@ func main() {
 			out, err = svc.GitCommit(ctx, activity.ActorUser, body.Path, body.Message)
 		case "discard":
 			out, err = svc.GitDiscard(ctx, activity.ActorUser, body.Path)
+		case "checkout":
+			out, err = svc.GitCheckout(ctx, activity.ActorUser, body.Path, body.Branch)
+		case "create-branch":
+			out, err = svc.GitCreateBranch(ctx, activity.ActorUser, body.Path, body.Branch)
 		default:
 			return c.JSON(http.StatusBadRequest, map[string]string{"error": "unknown op: " + body.Op})
 		}