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/milestones.py

@@ -53,6 +53,7 @@ async def get_milestone_in_project(project_id: int, milestone_id: int) -> Milest
             select(Milestone).where(
                 Milestone.id == milestone_id,
                 Milestone.project_id == project_id,
+                Milestone.deleted_at.is_(None),
             )
         )
         return result.scalars().first()
@@ -108,7 +109,10 @@ async def list_milestones(
 async def update_milestone(user_id: int, milestone_id: int, **fields: object) -> Milestone | None:
     async with async_session() as session:
         result = await session.execute(
-            select(Milestone).where(Milestone.id == milestone_id, Milestone.user_id == user_id)
+            select(Milestone).where(
+                Milestone.id == milestone_id, Milestone.user_id == user_id,
+                Milestone.deleted_at.is_(None),
+            )
         )
         milestone = result.scalars().first()
         if milestone is None: