Update project structure and enhance frontend functionality

- Added a new AGENTS.md file to document the project structure and conventions.
- Updated .gitignore to include node_modules and refined cursor rules.
- Introduced new backend and frontend components for improved map interactions, including context menus and controls.
- Enhanced API composables for better admin and authentication functionalities.
- Refactored existing components for cleaner code and improved user experience.
- Updated README.md to clarify production asset serving and user setup instructions.

.cursor/rules/project-conventions.mdc

@@ -0,0 +1,12 @@
+---
+description: Monorepo layout, backend/frontend locations, API/config pointers
+alwaysApply: true
+---
+
+# Project conventions
+
+- **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.
+- **Docs:** [docs/](docs/) (architecture, API, configuration, development, deployment). Some docs are in Russian.