feat(device): replace daily wakeHour with multi-time wakeTimes (minutes)

Frame settings now offer two update-frequency modes: "at specific times" or
"every X minutes". Times are stored as an int[] of minutes-since-midnight,
allowing multiple slots per day at minute granularity. Backend computes the
earliest upcoming slot for X-Interval-Ms and uses the most-recent-past slot
as the rotation-due boundary. PWA settings sheet has hour/minute/AM-PM
dropdowns with + Add / trash, a live "next update" preview, and a note
that changes only take effect at the device's next sync.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/test/components/DevicePicker.test.ts

@@ -27,7 +27,7 @@ const makeDevice = (overrides: Partial<Device> = {}): Device => ({
   name: 'Living Room',
   orientation: 'landscape',
   rotationIntervalMinutes: 60,
-  wakeHour: null,
+  wakeTimes: [],
   timezone: 'America/Chicago',
   uniquenessWindow: 30,
   linkedAt: '2026-01-01T00:00:00Z',