Archived several outdated reports (`Ping-Service_Impl_01-2026.md`, `Frontend_Integration_Status.md`, etc.) and added archival notes and references to updated documents. Introduced a centralized reference structure for tech stack documentation, consolidating files under `01_Architecture/Reference/Tech_Stack`. Added new resources (`Gradle_Kotlin_DSL_Primer`, `Kotlin_2-3-0_ReleaseNotes`) for improved project organization and clarity.
Added `/ping/sync` endpoint with timestamp-based Delta-Sync functionality to efficiently support offline-first clients. Extended `PingApi` and frontend clients (`PingApiClient`, `PingApiKoinClient`) with `syncPings`. Updated repository, service, and controller logic for sync handling, including new JPA query `findByCreatedAtAfter`. Adjusted test doubles and completed unit tests for backend and frontend alignment. Documented sync approach and API usage.
- Updated report to reflect the successful completion of Phase 1 ("Operation Tracer Bullet").
- Documented key achievements: security enhancement via OAuth2, microservice stabilization, and Docker optimizations.
- Added next steps for Phase 2, including frontend integration, observability improvements, and tracing setup.
Applied a unified header format to all documentation files for better status identification, referencing, and ownership tracking. Archived outdated roadmaps, reports, and journal entries. Updated playbooks with new responsibilities, lifecycle rules, and consistent handover formats to align with the new archiving strategy.
