Fix Phoenix.PubSub test setup and update Elixir to 1.18

- Updated all mix.exs files to require Elixir ~> 1.18 to match CI
- Fixed Phoenix.PubSub startup in test helper to avoid PG2 adapter issues
- Added application startup in supervisor tests to ensure proper initialization

Author: InvalidPathException

CLAUDE.md

@@ -0,0 +1,132 @@
+# Kafkaesque Development Commands
+
+> For comprehensive development guide including testing strategies and debugging, see [DEVELOPING.md](DEVELOPING.md)
+
+## Quick Start
+
+### Local Development
+```bash
+# Install dependencies
+mix deps.get
+
+# Run locally in development mode
+iex -S mix phx.server
+
+# Run tests
+mix test
+
+# Run tests with coverage
+mix test --cover
+
+# Run integration tests only
+mix test --only integration
+
+# Format code
+mix format
+
+# Check if code is formatted (CI/CD check)
+mix format --check-formatted
+
+# Run linter
+mix credo --strict
+
+# Check everything (compile, format, lint)
+mix lint
+```
+
+### Docker Development
+```bash
+# Build and start the container
+docker-compose up --build
+
+# Start in background
+docker-compose up -d
+
+# View logs
+docker-compose logs -f
+
+# Stop the container
+docker-compose down
+
+# Rebuild without cache (if needed)
+docker-compose build --no-cache
+```
+
+## API Testing
+
+### Inside Docker Container
+```bash
+# Health check
+docker exec kafkaesque-kafkaesque-1 curl http://localhost:4001/healthz
+
+# List topics
+docker exec kafkaesque-kafkaesque-1 curl http://localhost:4001/v1/topics
+
+# Create a topic
+docker exec kafkaesque-kafkaesque-1 curl -X POST http://localhost:4001/v1/topics \
+  -H 'Content-Type: application/json' \
+  -d '{"name":"events","partitions":1}'
+
+# Produce messages
+docker exec kafkaesque-kafkaesque-1 curl -X POST http://localhost:4001/v1/topics/events/records \
+  -H 'Content-Type: application/json' \
+  -d '{"acks":"leader","records":[{"key":"","value":"aGVsbG8="}]}'
+
+# Consume messages
+docker exec kafkaesque-kafkaesque-1 curl "http://localhost:4001/v1/topics/events/records?group=demo&offset=latest"
+```
+
+### From Host (when ports are exposed)
+```bash
+# Health check
+curl http://localhost:4001/healthz
+
+# API endpoints
+curl http://localhost:4001/v1/topics
+```
+
+## Build & Release
+
+### Create Production Release
+```bash
+MIX_ENV=prod mix release
+```
+
+### Run Release Locally
+```bash
+_build/prod/rel/kafkaesque/bin/kafkaesque start
+```
+
+## Protobuf Generation
+```bash
+mix proto.gen
+```
+
+## Cleanup
+
+### Stop all services
+```bash
+# Stop Docker containers
+docker-compose down
+
+# Remove volumes (careful - deletes data)
+docker-compose down -v
+
+# Clean build artifacts
+rm -rf _build deps
+```
+
+## Ports
+
+- **4000**: Phoenix Dashboard (LiveView)
+- **4001**: REST API Server  
+- **50051**: gRPC Server
+
+## Environment Variables
+
+See `docker-compose.yml` for full list. Key variables:
+- `SECRET_KEY_BASE`: Required for production
+- `DATA_DIR`: Where log files are stored
+- `OFFSETS_DIR`: Where consumer offsets are stored
+- `RETENTION_HOURS`: How long to keep messages (default: 168)
+- `LOG_LEVEL`: Logging verbosity (debug/info/warn/error)