feat(logging): integrate slog logging with env control and request/sync tracing

- Configure structured slog logger in cmd/server/main.go via LOG_LEVEL and DEBUG env vars
- Add HTTP API request logging middleware in internal/api/ with status and duration_ms
- Add WebSocket join/leave, event reception, and debounced SQLite flush tracing in docroom
- Document LOG_LEVEL and DEBUG settings in .env.example, compose.yaml, and docker-compose.yml

compose.yaml

@@ -14,6 +14,9 @@ services:
       - BASE_URL=${BASE_URL:-http://localhost:8080}
       - ALLOW_REGISTRATION=${ALLOW_REGISTRATION:-false}
       - LOG_LEVEL=${LOG_LEVEL:-info}
+      # Set LOG_LEVEL=debug or DEBUG=true for detailed request and sync logging
+      # - LOG_LEVEL=debug
+      # - DEBUG=true
       # Demo mode: if true, automatically seeds demo accounts admin/admin and user/user
       - MINDA_DEMO=${MINDA_DEMO:-false}
       # Optional SMTP / Mail Configuration (can also be configured in Admin UI)