fix: 🐛 keep dining hall open/closed status live (#501)

[wilyan09007]

Summary

The dining hall's Open/Closed status was derived from a selectedDate that is frozen when the app loads and a today captured once when the restaurant store is created, and nothing re-derived it on a timer. If you left a hall page open across an open→close transition, the status stayed stale (e.g. still showing Open after the hall had actually closed) until you refreshed the page.

This adds a live now clock to the restaurant store that ticks every 30 seconds while a hall page is mounted, and uses it as the reference time for the open/close window when you're viewing today. Any other selected day keeps comparing against the selected date, so its behavior is unchanged.

Changes

• useRestaurantStore: add a now: Date field (plus setNow) to the store
• useHallDerived: compare the open/close window against the live now when the selected day is today (falls back to selectedDate for any other day, preserving existing behavior)
• useRestaurantPage: tick now every 30s via setInterval while a hall page is mounted, cleaning up the interval on unmount

Testing Instructions

No local setup changes are needed beyond the usual dev environment.

1. Open the Anteatery or Brandywine page a few minutes before a meal-period boundary (an open→close or close→open time).
2. Leave the page open — do not refresh — and watch the status indicator (the colored dot + "Open"/"Closed" text, shown in the desktop controls and the mobile hero).
3. When the clock passes the boundary, the status should flip on its own within ~30s.
4. Sanity check that selecting a non-today date still shows its menu as before, and that selecting today reflects the current open/closed state.

Closes #501