fix(realtime): scope events to authorized users, authorize rooms, keep SSE alive

Phase 0 of the collaboration plan:
- Remove BroadcastToAll; task, task list and workspace folder events now
  only reach users who can see the resource. Task list events carry only
  the list ID, clients reload with their own permissions.
- Reject unauthenticated WebSocket/SSE connections (401). Every room join
  (URL room, JOIN_ROOM, SSE rooms) is checked via a room authorizer;
  /events/rooms requires login and only accepts the caller's own sseId.
- Reorder rejects tasks the caller cannot access or edit (IDOR).
- Lift the server WriteTimeout for SSE streams so they are not cut after 30s.
- Fix folder share removal sending DOC_DELETED to the share ID.
- Tests for all of the above; docs and flaw list updated.

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

Doku/api/rest.md

@@ -13,15 +13,15 @@ Basis: `/api/v1`. Antworten sind JSON; Fehler haben die Form `{"error": "Text"}`
 | POST | `/auth/login` | Anmeldung (`login`/`email`/`username`, `password`) → `{token, user}` |
 | POST | `/auth/quickstart` | Immer `403` (Gastzugang deaktiviert) |
 | POST | `/webhooks/ingest` | Aufgabe per Webhook anlegen, Token als `?token=`, `X-API-Key` oder Bearer. Body: `title`/`content`/`text`/`message`, `priority`, `source`, `tags`, `dueDate`; Klartext-Body wird als Inhalt genommen |
-| GET | `/ws`, `/ws/spaces/{id}`, `/ws/lists/{id}` | WebSocket, siehe [websocket.md](websocket.md) |
-| GET | `/events` | SSE-Fallback |
-| POST | `/events/rooms` | SSE-Räume beitreten/verlassen ([FLAW-02](../flaws.md)) |
+| GET | `/ws`, `/ws/spaces/{id}`, `/ws/lists/{id}` | WebSocket, siehe [websocket.md](websocket.md); Token als `?token=` nötig |
+| GET | `/events` | SSE-Fallback; Token als `?token=` nötig |
 
 ## Konto und Allgemeines (angemeldet)
 
 | Methode | Pfad | Zweck |
 |---|---|---|
 | GET | `/auth/me` | Benutzer und Kennzahlen |
+| POST | `/events/rooms` | SSE-Raum beitreten/verlassen (`sseId`, `room`, `action`); nur eigene `sseId`, nur Räume mit Lesezugriff |
 | POST | `/auth/logout` | Token sperren |
 | POST | `/auth/revoke-all` | Alle Sitzungen beenden (`token_version` +1) |
 | PATCH | `/auth/settings` | `displayName`, `email`, `password`, `avatarUrl`, `alarmChannels`, `alarmEmail`, `discordWebhookUrl`, `customWebhookUrl`, `notifyBeforeMinutes` |