Add time-based day progress bar to dashboards

Replaces block-count progress with a wall-clock progress bar driven by
configurable day start/end hours on each schedule template.

- ScheduleTemplate: add day_start_time / day_end_time (TIME, nullable)
- Startup migration: idempotent ALTER TABLE for existing DBs
- Dashboard snapshot: includes day_start_time / day_end_time from template
- Admin → Schedules: time pickers in block editor to set day hours
- Dashboard view: time-based progress bar with start/current/end labels
- TV view: full-width day progress strip between header and main content

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

backend/app/routers/schedules.py

@@ -42,6 +42,8 @@ async def create_template(
         name=body.name,
         child_id=body.child_id,
         is_default=body.is_default,
+        day_start_time=body.day_start_time,
+        day_end_time=body.day_end_time,
     )
     db.add(template)
     await db.flush()  # get template.id before adding blocks