Live dining hall hours from UMD's published schedule

[aleczzhang]

Summary

Dining hall hours were hardcoded to one week ("4/27–5/3"), so the app showed halls as open on breaks (e.g. Yahentamitsi during fall break, Oct 10–12). This serves UMD Dining's published day-by-day hours and uses them in the app.

Backend

• hours.py fetches the public Google Sheet that dining.umd.edu/hours/open-now reads, parses each hall × meal × date, and caches it (refreshes at most hourly; keeps the last good copy if Google fails, retries after 5 min).
• GET /api/hours?start=YYYY-MM-DD&days=N (defaults: today on campus, 14 days; max 60). [] for a date = closed all day; a missing date = unknown. 503 only if the sheet has never loaded.
• Unclear cells ("TBD", blanks, times without am/pm) are treated as unknown, not guessed.

App

• HallHoursService fetches 21 days, caches to UserDefaults for offline, refreshes when the hall picker appears (at most hourly).
• Hall cards use live hours when the day is covered, otherwise fall back to the existing hardcoded schedule.
• Closed cards now say "Opens Tue at 4 PM" / "Opens tomorrow at 7 AM" by looking ahead up to 7 days.

Notes

• Merging deploys the API (deploy-api.yml); the app falls back to the hardcoded hours until /api/hours is live.
• Times use the device's calendar, same as before, so a device outside Eastern time is off.
• Known follow-up: a midnight close would be labelled "12 PM" by the existing time formatter (no hall closes at midnight in the current sheet).
• Merge this before fix/empty-state-swipe-dining-hall-jump; their HomeView.swift changes don't conflict.

Testing

• Backend: 30 new tests in tests/test_hours.py; full suite 179 passed; ruff clean.
• App: 13 new tests (HallHoursTests); full app suite passed.
• Checked against the live sheet: Yahentamitsi closed Oct 10–12, dinner-only Oct 13.

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