fix(schedulers): wire recurring-task spawn + deliver event reminders

Drift-audit Group 2 (Phase-8 amputation — live wiring, no consumer):

- Recurring tasks never recurred: spawn_recurring_tasks() had no caller.
  Register it as a 15-min interval job in the event scheduler (which
  app.py already starts/stops). Also add a deleted_at IS NULL guard to
  the spawn query in the same change, so a trashed recurring parent can
  never resurrect children once the sweep is live.
- Event reminders were stamped reminder_sent_at but never delivered.
  _fire_reminders now creates an 'event_reminder' in-app notification
  before stamping, so a delivery failure stays retryable. Frontend
  NotificationsPanel renders the new type (⏰ + message); message logic
  pulled into a notifMessage() helper.
- Remove the dead _fire_push_notif no-op stub (push left in Phase 8) and
  its three create_task call sites — no more throwaway tasks per share.

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

src/fabledassistant/services/notifications.py

@@ -266,12 +266,6 @@ async def create_in_app_notification(user_id: int, notif_type: str, payload: dic
         return n
 
 
-async def _fire_push_notif(user_id: int, title: str, body: str, url: str) -> None:
-    # Push delivery was removed alongside the chat subsystem (Phase 8).
-    # In-app notifications still flow through the bell-icon feed.
-    return None
-
-
 async def _fire_share_email(user_id: int, subject: str, body_text: str) -> None:
     try:
         if not await is_smtp_configured():
@@ -325,7 +319,6 @@ async def notify_project_shared(
             "invited_by": inviter.username,
             "url": url,
         })
-        asyncio.create_task(_fire_push_notif(uid, "Project shared with you", msg, url))
         asyncio.create_task(_fire_share_email(uid, f"[Fabled] {inviter.username} shared a project with you", msg))
 
 
@@ -361,7 +354,6 @@ async def notify_note_shared(
             "invited_by": inviter.username,
             "url": url,
         })
-        asyncio.create_task(_fire_push_notif(uid, "Note shared with you", msg, url))
         asyncio.create_task(_fire_share_email(uid, f"[Fabled] {inviter.username} shared a note with you", msg))
 
 
@@ -385,7 +377,6 @@ async def notify_group_added(
         "invited_by": inviter.username,
         "url": url,
     })
-    asyncio.create_task(_fire_push_notif(target_user_id, "Added to a group", msg, url))
     asyncio.create_task(_fire_share_email(target_user_id, "[Fabled] You've been added to a group", msg))