feat(tasks): repeating tasks (daily, weekly, monthly, yearly)

- recurrence on tasks, set in the detail dialog; 🔁 on rows and Kanban cards
- Completing a repeating task (detail, list, Kanban drag to done, note
  checkbox) creates the next one: title, tags, priority, notes, list,
  assignees and rule copied, subtasks reset, first open column, due date
  one interval later (month end clamped); pushed live as TASK_CREATED
- Each task spawns at most once (re-open + complete makes no duplicate)
- Export/import keep the rule (Obsidian Tasks "🔁 every week", JSON field)

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

internal/api/server.go

@@ -43,6 +43,10 @@ func NewServer(cfg *config.Config, store *storage.Store, wsHub *ws.Hub, staticFS
 		notifier: collab.NewNotifier(),
 	}
 	wsHub.SetRoomAuthorizer(srv.canJoinRoom)
+	// Next occurrences of repeating tasks appear live on every connected client
+	store.OnTaskCreated = func(th *domain.Thought) {
+		srv.wsHub.BroadcastToUsers(srv.taskAudience(th), "TASK_CREATED", th)
+	}
 	go srv.startAlarmTicker()
 	go srv.startCompaction()
 	return srv
@@ -957,6 +961,7 @@ func (s *Server) handleUpdateThought(w http.ResponseWriter, r *http.Request) {
 		Subtasks     *[]domain.SubTask `json:"subtasks"`
 		Tags         *[]string         `json:"tags"`
 		Assignees    *[]string         `json:"assignees"`
+		Recurrence   *string           `json:"recurrence"`
 	}
 	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
 		writeError(w, http.StatusBadRequest, "Ungültiges JSON")
@@ -964,6 +969,13 @@ func (s *Server) handleUpdateThought(w http.ResponseWriter, r *http.Request) {
 	}
 
 	before, _ := s.store.GetThoughtByID(userID, thoughtID)
+	// The rule is set first, so completing a task in the same request already repeats it
+	if req.Recurrence != nil {
+		if err := s.store.SetTaskRecurrence(userID, thoughtID, strings.TrimSpace(*req.Recurrence)); err != nil {
+			writeStoreError(w, http.StatusBadRequest, err)
+			return
+		}
+	}
 	updated, err := s.store.UpdateThoughtDetails(userID, thoughtID, req.Content, req.IsCompleted, req.DueDate, req.Priority, req.TaskListID, req.KanbanStatus, req.Notes, req.Subtasks, req.Tags)
 	if err != nil {
 		writeStoreError(w, http.StatusBadRequest, err)