Add Android agent activity notifications

[HorusGoul]

Summary

• Add Android variants to the relay device contracts and relay persistence, including channel metadata and a migration for Android mobile devices.
• Register Android devices with native FCM tokens, create Agent Activity notification channels, and handle Android foreground notification behavior/deep-link payloads.
• Update mobile settings and web mobile-client labels for Android while keeping iOS Live Activity fanout restricted to iOS targets.

Verification

• vp check
• vp run typecheck
• vp test run apps/mobile/src/features/agent-awareness/remoteRegistration.test.ts apps/mobile/src/features/agent-awareness/notificationNavigation.test.ts apps/mobile/src/features/agent-awareness/androidNotifications.test.ts packages/contracts/src/relay.test.ts apps/web/src/components/clerk/MobileClientsUserProfilePage.logic.test.ts infra/relay/src/agentActivity/Devices.test.ts
• vp run lint:mobile

Closes #6