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/models/schedule.py

@@ -14,6 +14,8 @@ class ScheduleTemplate(TimestampMixin, Base):
     )
     name: Mapped[str] = mapped_column(String(100), nullable=False)
     is_default: Mapped[bool] = mapped_column(Boolean, default=False)
+    day_start_time: Mapped[time | None] = mapped_column(Time, nullable=True)
+    day_end_time: Mapped[time | None] = mapped_column(Time, nullable=True)
 
     user: Mapped["User"] = relationship("User", back_populates="schedule_templates")  # noqa: F821
     child: Mapped["Child | None"] = relationship("Child")  # noqa: F821