fix(soft-delete): filter trashed rows across read/write paths

Drift-audit Group 3 (soft-delete lifecycle gaps). Trashed rows were
leaking into reads and being mutated/resurrected by writes:

- update SELECTs now exclude trashed rows: update_milestone,
  update_project, update_event, and get_milestone_in_project (the latter
  backs all four milestone routes). Mutating a trashed row silently
  persisted and reappeared on restore.
- MCP get_recent (notes/projects/events) and list_tags now filter
  deleted_at IS NULL, so trashed items stop surfacing in the agent's
  bootstrap context and tag counts.
- convert_task_to_note clears recurrence_rule + recurrence_next_spawn_at
  so a demoted note can't spawn children via the (now-live) sweep.
- caldav pull skips locally-trashed events (by caldav_uid) instead of
  resurrecting them via update or creating a duplicate live copy.
- trash _cascade now stamps the FULL sub-task subtree (iterative descent),
  not just direct children, so deeply nested sub-tasks restore as one
  batch. Test updated for the new descent query.

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

src/fabledassistant/services/projects.py

@@ -79,7 +79,10 @@ async def list_projects(user_id: int, status: str | None = None) -> list[Project
 async def update_project(user_id: int, project_id: int, **fields: object) -> Project | None:
     async with async_session() as session:
         result = await session.execute(
-            select(Project).where(Project.id == project_id, Project.user_id == user_id)
+            select(Project).where(
+                Project.id == project_id, Project.user_id == user_id,
+                Project.deleted_at.is_(None),
+            )
         )
         project = result.scalars().first()
         if project is None: