Add Morning Routine to Admin and TV greeting state

Adds a per-user Morning Routine item list that appears in the TV
dashboard Activities panel during the "Good Morning" countdown
(before the first block starts).

- morning_routine_items table (auto-created on startup)
- CRUD API at /api/morning-routine (auth-required)
- Items included in the public DashboardSnapshot so TV gets them
  without auth
- Morning Routine section in Admin page (same add/edit/delete UX
  as subject options)
- TV Activities column shows routine items when no block is active,
  switches to subject options once a block starts

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/schemas/session.py

@@ -46,3 +46,4 @@ class DashboardSnapshot(BaseModel):
     is_paused: bool = False          # whether the current block's timer is paused
     day_start_time: time | None = None
     day_end_time: time | None = None
+    morning_routine: list[str] = []  # text items shown on TV during greeting state