feat: link dialog finds bullets of all notes; richer sample data with help notes, deep nesting and linked to-dos

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/api/handlers_lists.go

@@ -38,9 +38,9 @@ func (s *Server) handleGetListByID(w http.ResponseWriter, r *http.Request) {
 func (s *Server) handleCreateList(w http.ResponseWriter, r *http.Request) {
 	userID := auth.GetUserID(r.Context())
 	var req struct {
-		Title    string `json:"title"`
+		Title    string  `json:"title"`
 		Icon     *string `json:"icon"` // "" = no icon; missing = the default
-		ListType string `json:"listType"`
+		ListType string  `json:"listType"`
 	}
 	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
 		writeError(w, http.StatusBadRequest, "Ungültiges JSON")