fix(caldav): point-event round-trip, recurrence push, delete propagation

Drift-audit Group 5 #7/#8 + Group 7 (CalDAV write-path):

- Point events no longer fabricate a 60-min DTEND: caldav.create_event emits
  DTSTART-only when there's no end and no duration, so the next pull doesn't
  read it back as duration_minutes=60 and silently lengthen the event.
- Recurrence edits now propagate: caldav.update_event gains a recurrence param
  (sentinel = leave unchanged; value/empty = set/clear RRULE), and _push_update
  passes the local event's rule so a changed/cleared RRULE isn't overwritten
  by the stale remote rule on the next pull.
- Event deletions propagate to CalDAV: trash.delete captures an event's
  caldav_uid before soft-deleting and fires _push_delete, so a UI/MCP delete
  removes the remote copy instead of leaving it to linger. (delete_event the
  service primitive is kept — still tested/usable — rather than removed.)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/fabledassistant/services/trash.py

@@ -149,11 +149,28 @@ async def delete(user_id: int, entity_type: str, entity_id: int) -> str | None:
     """
     batch = str(uuid.uuid4())
     now = datetime.now(timezone.utc)
+    caldav_event: tuple[str, str] | None = None
     async with async_session() as session:
         if not await _exists_alive(session, user_id, entity_type, entity_id):
             return None
+        # Capture CalDAV linkage before soft-deleting so we can propagate the
+        # deletion to the external server (the row stays present locally).
+        if entity_type == "event":
+            row = (await session.execute(
+                select(Event.caldav_uid, Event.title).where(
+                    Event.id == entity_id, Event.user_id == user_id
+                )
+            )).first()
+            if row and row[0]:
+                caldav_event = (row[0], row[1])
         await _cascade(session, user_id, entity_type, entity_id, batch, now)
         await session.commit()
+    # Without this the soft-delete only hides the event locally and the remote
+    # copy lingers forever (and re-appears on any client syncing that server).
+    if caldav_event:
+        import asyncio
+        from fabledassistant.services.events import _push_delete
+        asyncio.create_task(_push_delete(caldav_event[0], caldav_event[1], user_id))
     return batch