[codex] add analytics preference tracking

[jjoonleo]

Summary

• Add a config-gated Firebase Analytics service and opt-in analytics preference flow.
• Add local/account analytics preference data sources, repository, use cases, and My Page toggle.
• Track the first schedule_created product usage event from schedule creation.
• Document the analytics event catalog, preference API expectations, privacy/release checklist updates, and ADRs.

Validation

• dart run build_runner build --delete-conflicting-outputs
• flutter analyze
• flutter test
• After the final DI cleanup: flutter test test/core/services/fallback_alarm_notification_service_test.dart test/presentation/my_page/my_page_screen_test.dart

Notes

• Analytics collection remains disabled unless ONTIME_ANALYTICS_ENABLED=true and the loaded preference is confirmed enabled.
• Backend issue DevKor-github/OnTime-back#318 is closed; hosted privacy policy issue DevKor-github/OnTime-back#319 remains release-gated.

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[github-actions]

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