Local Notifications Scheduler

One on-device reminder engine, owned centrally, with a narrow API. The local DB is the source of truth; the OS pending set is a disposable cache. Every scheduling change flows through one pure-then-reconcile path so the whole engine is verifiable off-device. Applies whenever you schedule, cancel, or reason about local notifications.

Read the reference for the task at hand:

• references/notification-gateway-port.md — the port contract, the two adapters, channels/grouping/deep-link payload rules.
• references/scheduler-and-recurrence-rules.md — pure ReminderScheduler.compute diff, recurrence/DST math, deterministic IDs, budgeting, the full test matrix.
• references/platform-boot-exact-alarms-oem.md — boot re-arm, exact-alarm degradation, background-isolate safety, Android manifest/Gradle, the OEM survival matrix.

Run scripts/check-single-fln-import.sh, scripts/check-scheduler-purity.sh, scripts/check-adhoc-schedule-calls.sh, and scripts/check-manifest-permissions.sh before a PR.

Non-negotiable rules