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.

.cursor/rules/project-conventions.mdc

@@ -8,7 +8,7 @@ alwaysApply: true
 - **Monorepo:** Go backend + Nuxt 3 frontend. Backend: `cmd/hnh-map/`, `internal/app/`. Frontend source: `frontend-nuxt/`; production static output: `frontend/` (build artifact from `frontend-nuxt/`, do not edit).
 - **Changing API:** Update `internal/app/` (e.g. `api.go`, `map.go`) and [docs/api.md](docs/api.md); frontend uses composables in `frontend-nuxt/composables/` (e.g. `useMapApi.ts`).
 - **Changing config:** Update [.env.example](.env.example) and [docs/configuration.md](docs/configuration.md).
-- **Local run / build:** [docs/development.md](docs/development.md), [CONTRIBUTING.md](CONTRIBUTING.md). Dev ports: frontend 3000, backend 3080; prod: 8080.
+- **Local run / build:** [docs/development.md](docs/development.md), [CONTRIBUTING.md](CONTRIBUTING.md). Dev ports: frontend 3000, backend 3080; prod: 8080. Build, test, lint, and format run via Docker (Makefile + docker-compose.tools.yml).
 - **Docs:** [docs/](docs/) (architecture, API, configuration, development, deployment). Some docs are in Russian.
 - **Coding:** Write tests first before implementing any functionality.
 - **Running tests:** When the user asks to run tests or to verify changes, use the run-tests skill: [.cursor/skills/run-tests/SKILL.md](.cursor/skills/run-tests/SKILL.md).

.cursor/skills/run-tests/SKILL.md

@@ -12,42 +12,20 @@ description: Runs backend (Go) and frontend (Vitest) tests for the hnh-map monor
 
 ## What to run
 
-This repo has two test suites. Run the one(s) that match the changed code, or both if unsure.
+Tests run **in Docker** via the Makefile; no local Go or Node is required.
 
-### Backend (Go)
+From the repo root, use:
 
-From repo root:
+- **Both backend and frontend:** `make test` (runs backend then frontend tests in Docker).
+- **Backend only:** `make test-backend`
+- **Frontend only:** `make test-frontend`
 
-```bash
-make test
-```
-
-Or:
-
-```bash
-go test ./...
-```
-
-Uses temp dirs and in-memory DBs; no external services needed.
-
-### Frontend (Vitest)
-
-From repo root:
-
-```bash
-npm --prefix frontend-nuxt run test
-```
-
-Or from `frontend-nuxt/`:
-
-```bash
-npm test
-```
+These use `docker-compose.tools.yml`; the first run may build the backend-tools image.
 
 ## Scope
 
-- **Backend-only changes** (e.g. `internal/`, `cmd/`): run `make test`.
-- **Frontend-only changes** (e.g. `frontend-nuxt/`): run `npm --prefix frontend-nuxt run test`.
-- **Both or unclear**: run backend then frontend.
+- **Backend-only changes** (e.g. `internal/`, `cmd/`): run `make test-backend`.
+- **Frontend-only changes** (e.g. `frontend-nuxt/`): run `make test-frontend`.
+- **Both or unclear**: run `make test`.
 
 Report pass/fail and any failing test names or errors.