Add CHANGELOG.md and update documentation process

- Create comprehensive CHANGELOG.md with all recent changes
- Add mandatory instruction in CLAUDE.md to update changelog
- Follow Keep a Changelog format for consistency
- Document all changes from v0.1.0 to current v0.2.0

Co-Authored-By: Claude <noreply@anthropic.com>

CHANGELOG.md

@@ -0,0 +1,55 @@
+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [Unreleased]
+
+## [0.2.0] - 2025-07-26
+
+### Added
+- Redis-based distributed PubSub for real-time updates across replicas
+- PgBouncer connection pooling for efficient database connections
+- Distributed caching with Redis (query, device, symbol caches)
+- Distributed rate limiting with Redis using sliding window algorithm
+- Graceful shutdown handling with connection draining
+- PodDisruptionBudget for zero-downtime deployments
+- Signal handler for proper SIGTERM handling
+- Comprehensive health checks for Kubernetes probes
+- Docker build optimizations with better layer caching
+- Concurrency control in CI/CD pipeline
+
+### Changed
+- Moved from ETS to Redis for caching when REDIS_URL is available
+- Updated Kubernetes deployment to use StatefulSet with stable networking
+- Simplified Dockerfile by removing Node.js dependencies
+- Improved CI/CD to not wait for rollout completion
+- Enhanced shutdown process to be silent (no user notifications)
+- Optimized Docker image size (removed ~150MB)
+
+### Fixed
+- PgBouncer database connection issues with SKIP_DB_CREATE
+- Redis connection errors by removing invalid pool_size option
+- Compilation warnings by grouping handle_info clauses
+- ShutdownHandler interfering with application startup
+- DeviceCache startup timing issues with Redis
+- Docker permission errors with non-root user
+
+### Removed
+- Node.js and npm from Docker image (using standalone ESBuild/Tailwind)
+- Complex BuildKit features that were slowing builds
+- Multi-platform Docker builds (simplified to amd64 only)
+
+## [0.1.0] - 2023-12-17
+
+### Added
+- Initial release
+- APRS-IS network connection with reconnection logic
+- Real-time packet processing with GenStage pipeline
+- Phoenix LiveView map interface
+- PostGIS geographic data storage
+- Background job processing with Oban
+- ETS-based local caching
+- Basic rate limiting

CLAUDE.md

@@ -116,9 +116,14 @@ Tests use comprehensive mocking to prevent external connections:
 
 ## Important Documentation Updates
 
-- **MANDATORY**: Whenever you implement improvements or changes to the system, update `/docs/improvement-todos.md` with:
+- **MANDATORY**: Whenever you implement improvements or changes to the system:
-  - Mark completed items as done with the implementation date
+  1. Update `/CHANGELOG.md` with:
-  - Add any new improvements discovered during implementation
+     - Add new entries under `[Unreleased]` section
+     - Use categories: Added, Changed, Fixed, Removed
+     - Be specific and user-focused in descriptions
+  2. Update `/docs/improvement-todos.md` with:
+     - Mark completed items as done with the implementation date
+     - Add any new improvements discovered during implementation
   - Update priority levels based on new insights
   - Document any technical decisions or trade-offs made
 - This ensures continuity across sessions and helps track progress on system improvements