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/backend-go.mdc

@@ -0,0 +1,11 @@
+---
+description: Go style and backend layout (internal/app)
+globs: "**/*.go"
+alwaysApply: false
+---
+
+# Backend (Go)
+
+- 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.