Enhance development workflow with Docker integration

- Updated CONTRIBUTING.md to clarify the use of Makefile targets for running tasks inside Docker, eliminating the need for local Go or Node installations.
- Introduced docker-compose.tools.yml for backend and frontend tools, allowing for streamlined testing, linting, and formatting.
- Created Dockerfile.tools to set up a Go environment with necessary tools for testing and linting.
- Modified Makefile to include separate targets for backend and frontend tests, improving clarity and usability.
- Updated documentation in development.md and testing.md to reflect the new Docker-based workflow for running tests and development tasks.

docker-compose.tools.yml

@@ -0,0 +1,21 @@
+# One-off tools: test, lint, fmt. Use with: docker compose -f docker-compose.tools.yml run --rm <service> <cmd>
+# Source is mounted so commands run against current code.
+
+services:
+  backend-tools:
+    build:
+      context: .
+      dockerfile: Dockerfile.tools
+    volumes:
+      - .:/hnh-map
+    # Default command; override when running (e.g. go test ./..., golangci-lint run).
+    command: ["go", "test", "./..."]
+
+  frontend-tools:
+    image: node:20-alpine
+    working_dir: /app
+    volumes:
+      - ./frontend-nuxt:/app
+      - /app/node_modules
+    # Default command; override when running (e.g. npm test, npm run lint).
+    command: ["npm", "test"]