Update project configuration and documentation

- Modified .gitignore to retain rules directory while excluding other cursor files.
- Updated backend-go.mdc to clarify compatibility notes.
- Enhanced project-conventions.mdc with guidelines on coding practices and running tests.
- Added SKILL.md for detailed instructions on running backend and frontend tests in the hnh-map monorepo.

.cursor/rules/backend-go.mdc

@@ -8,4 +8,4 @@ alwaysApply: false
 
 - Entry point: [cmd/hnh-map/main.go](cmd/hnh-map/main.go). All app logic in `internal/app/` (package `app`): `app.go`, `auth.go`, `api.go`, `map.go`, `tile.go`, `admin_*.go`, `client*.go`, `migrations.go`, etc.
 - Use `go fmt ./...` before committing. Run `go test ./...` when changing behaviour.
-- Compatibility note: keep in mind [hnh-auto-mapper-server](https://github.com/APXEOLOG/hnh-auto-mapper-server) when touching client protocol or public API.
+- Compatibility note: keep in mind [hnh-auto-mapper-server](https://github.com/APXEOLOG/hnh-auto-mapper-server) when touching client protocol or public API.

.cursor/rules/project-conventions.mdc

@@ -10,3 +10,5 @@ alwaysApply: true
 - **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.
 - **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).