fix(android): reschedule alarms on device reboot via BootReceiver

[KashifKhn]

Summary

• Adds BootReceiver.kt — a BroadcastReceiver that handles BOOT_COMPLETED and LOCKED_BOOT_COMPLETED intents and reschedules all future alarms via NativeAlarmScheduler
• Extends NativeAlarmStore to persist full scheduling metadata (title, body, sound, scheduledTimeMillis) as a JSON entry so BootReceiver has everything it needs without involving Flutter
• Registers BootReceiver in AndroidManifest.xml with the correct intent filters (BOOT_COMPLETED + LOCKED_BOOT_COMPLETED)

Acceptance Criteria

• BootReceiver Kotlin class exists and handles BOOT_COMPLETED / LOCKED_BOOT_COMPLETED intents
• BootReceiver is registered in AndroidManifest.xml with the correct intent filters
• RECEIVE_BOOT_COMPLETED permission is declared in the manifest
• After a reboot, all enabled alarms fire at their correct next time without the user opening the app

Closes #10

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Project	Deployment	Actions	Updated (UTC)
drawbell	Ready	Preview, Comment	Apr 1, 2026 0:37am

[KashifKhn]

Potential bug (high impact for reboot reliability): repeating alarms may be lost after reboot if their last scheduled time is already in the past.

In BootReceiver.onReceive, entries are skipped when entry.scheduledTimeMillis <= now, and NativeAlarmStore entries only persist a single scheduledTimeMillis (not repeat metadata like hour/minute/repeatDays for normal entries).

Scenario:

1. A repeating alarm is scheduled for 08:00
2. Device reboots at 09:00
3. BootReceiver skips the stored entry as past
4. The next repeat is never re-armed unless/until the app is opened (which later calls rescheduleAll())

This seems to violate the acceptance criterion that enabled alarms should fire correctly after reboot without opening the app.