Improve test infrastructure and organization

- Add test-runner stage to Dockerfile for isolated test execution
- Refactor Makefile test targets: separate unit and integration tests
- Unit tests now run on host (fast, no containers required)
- Integration tests run in containers matching production environment
- Add dedicated 'tests' service to docker-compose.yml
- Update test-integration target to use containerized test runner
- Improve service health checks and wait conditions
- Add test environment variables for consistent testing

This change separates unit tests (fast, local) from integration tests
(full environment, containerized) for better developer experience
and more reliable CI/CD pipelines.

docker-compose.yml

@@ -65,6 +65,48 @@ services:
       retries: 3
       start_period: 10s
 
+  # Integration Tests - runs against containerized app and db
+  tests:
+    build:
+      context: .
+      dockerfile: ./Dockerfile
+      target: test-runner
+    container_name: bookhoard_tests
+    environment:
+      # Database Configuration
+      DATABASE_HOST: db
+      DATABASE_PORT: 5432
+      DATABASE_USER: postgres
+      DATABASE_PASSWORD: ${DBPASS}
+      DATABASE_NAME: bookhoard
+
+      # Application Configuration
+      JWT_SECRET: ${JWT_SECRET}
+      SERVER_PORT: 8765
+
+      # Test Configuration
+      TEST_MODE: "true"
+      RATE_LIMIT_ENABLED: "false"
+      REQUESTS_PER_MINUTE: 1000
+
+      # Conversion Service Configuration
+      BOOKHOARD_CONVERSION_CACHE_DIR: /app/cache/kepub
+      BOOKHOARD_CONVERSION_TOOL: /usr/bin/kepubify
+      BOOKHOARD_CONVERSION_CACHE_TTL: 24h
+
+      # Test upload path (inside container)
+      TEST_UPLOAD_PATH: /app/uploads
+    depends_on:
+      db:
+        condition: service_healthy
+      app:
+        condition: service_healthy
+    volumes:
+      - ./uploads:/app/uploads
+      - bookhoard_conversion_cache:/app/cache/kepub
+    profiles:
+      - tests
+
 # Named Volumes
 volumes:
   postgres_data: