feat(workspace): add GET /branches endpoint

internal/workspace/dto.go

@@ -115,3 +115,7 @@ func toFileStatusResp(f git.FileStatus) fileStatusResp {
 type commitResp struct {
 	SHA string `json:"sha"`
 }
+
+type branchListResp struct {
+	Branches []string `json:"branches"`
+}

internal/workspace/handler.go

@@ -62,6 +62,7 @@ func (h *Handler) Mount(r chi.Router) {
 
 		r.Get("/worktrees", h.listWorktrees)
 		r.Post("/worktrees", h.createWorktree)
+		r.Get("/branches", h.listBranches)
 	})
 	r.With(auth).Route("/api/v1/worktrees/{wtID}", func(r chi.Router) {
 		r.Delete("/", h.deleteWorktree)
@@ -340,6 +341,25 @@ func (h *Handler) createWorktree(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, http.StatusCreated, toWorktreeResp(wt))
 }
 
+func (h *Handler) listBranches(w http.ResponseWriter, r *http.Request) {
+	c, err := h.caller(r)
+	if err != nil {
+		writeErr(w, r, err)
+		return
+	}
+	id, err := parseUUID(chi.URLParam(r, "wsID"))
+	if err != nil {
+		writeErr(w, r, err)
+		return
+	}
+	branches, err := h.ws.ListBranches(r.Context(), c, id)
+	if err != nil {
+		writeErr(w, r, err)
+		return
+	}
+	writeJSON(w, http.StatusOK, branchListResp{Branches: branches})
+}
+
 func (h *Handler) deleteWorktree(w http.ResponseWriter, r *http.Request) {
 	c, err := h.caller(r)
 	if err != nil {

internal/workspace/handler_test.go

@@ -49,7 +49,7 @@ func (f *fakeWS) GetCredentialMeta(_ context.Context, _ Caller, _ uuid.UUID) (*C
 }
 
 func (f *fakeWS) ListBranches(_ context.Context, _ Caller, _ uuid.UUID) ([]string, error) {
-	return nil, nil
+	return []string{"main", "develop"}, nil
 }
 
 // fakeResolver 把固定 token 解码为 uuid（沿 internal/project handler_test.go 模式）。
@@ -86,3 +86,26 @@ func TestHandler_CreateWorkspace_Smoke(t *testing.T) {
 	r.ServeHTTP(w, req)
 	require.Equal(t, http.StatusCreated, w.Code)
 }
+
+func TestHandler_ListBranches_Smoke(t *testing.T) {
+	t.Parallel()
+	ws := &fakeWS{}
+	uid := uuid.New()
+	tok := "tok-branches"
+	resolver := &fakeResolver{valid: map[string]uuid.UUID{tok: uid}}
+	h := NewHandler(ws, nil, nil, resolver, fakeAdmin{})
+	r := chi.NewRouter()
+	r.Use(middleware.RequestID)
+	h.Mount(r)
+
+	wsID := uuid.New()
+	req := httptest.NewRequest("GET", "/api/v1/workspaces/"+wsID.String()+"/branches", nil)
+	req.Header.Set("Authorization", "Bearer "+tok)
+	w := httptest.NewRecorder()
+	r.ServeHTTP(w, req)
+	require.Equal(t, http.StatusOK, w.Code)
+
+	var resp branchListResp
+	require.NoError(t, json.NewDecoder(w.Body).Decode(&resp))
+	require.Equal(t, []string{"main", "develop"}, resp.Branches)
+}