Add configuration files and update project documentation

- Introduced .editorconfig for consistent coding styles across the project.
- Added .golangci.yml for Go linting configuration.
- Updated AGENTS.md to clarify project structure and components.
- Enhanced CONTRIBUTING.md with Makefile usage for common tasks.
- Updated Dockerfiles to use Go 1.24 and improved build instructions.
- Refined README.md and deployment documentation for clarity.
- Added testing documentation in testing.md for backend and frontend tests.
- Introduced Makefile for streamlined development commands and tasks.

CONTRIBUTING.md

@@ -4,18 +4,42 @@
 
 Clone the repository and run the project locally (see [Development](docs/development.md)):
 
-- **Option A:** Docker Compose for development: `docker compose -f docker-compose.dev.yml up` (frontend on 3000, backend on 3080).
+- **Option A:** Docker Compose for development: `docker compose -f docker-compose.dev.yml up` (or `make dev`). Frontend on 3000, backend on 3080.
 - **Option B:** Run Go backend from the repo root (`go run ./cmd/hnh-map -grids=./grids -port=8080`) and Nuxt separately (`cd frontend-nuxt && npm run dev`). Ensure the frontend can reach the backend (proxy or same host).
 
 ## Code layout
 
-- **Backend:** Entry point is `cmd/hnh-map/main.go`. All application logic lives in `internal/app/` (package `app`): `app.go`, `auth.go`, `api.go`, `handlers_redirects.go`, `client.go`, `client_grid.go`, `client_positions.go`, `client_markers.go`, `admin_*.go`, `map.go`, `tile.go`, `topic.go`, `migrations.go`.
-- **Frontend:** Nuxt 3 app in `frontend-nuxt/` (pages, components, composables, layouts, server, plugins, `public/gfx`). It is served by the Go backend at root `/` with baseURL `/`.
+The backend follows a layered architecture: **Store → Services → Handlers**.
 
-## Formatting and tests
+- **Backend:** Entry point is `cmd/hnh-map/main.go`. Application logic lives in `internal/app/`:
+  - `app.go` — `App` struct, domain types, SPA serving, constants.
+  - `router.go` — route registration.
+  - `topic.go` — pub/sub for real-time updates.
+  - `migrations.go` — database migrations.
+  - `store/` — bbolt database access layer (`db.go`, `buckets.go`).
+  - `services/` — business logic (`auth.go`, `map.go`, `admin.go`, `client.go`, `export.go`).
+  - `handlers/` — HTTP handlers (`api.go`, `auth.go`, `map.go`, `client.go`, `admin.go`, `tile.go`, `handlers.go`, `response.go`).
+  - `apperr/` — domain error types.
+  - `response/` — shared JSON response helpers.
+- **Frontend:** Nuxt 3 app in `frontend-nuxt/` (pages, components, composables, layouts, plugins, `public/gfx`). It is served by the Go backend at root `/` with baseURL `/`.
 
-- Go: run `go fmt ./...` before committing.
-- Add or update tests if you change behaviour; run `go test ./...` if tests exist.
+## Formatting, linting, and tests
+
+Use Makefile targets for common tasks:
+
+```bash
+make fmt      # Format all code (Go + frontend)
+make lint     # Run Go linter (golangci-lint) and frontend ESLint
+make test     # Run Go tests
+```
+
+Or run manually:
+
+- Go: `go fmt ./...` and `golangci-lint run`
+- Frontend: `npm --prefix frontend-nuxt run lint` and `npm --prefix frontend-nuxt run format`
+- Tests: `go test ./...`
+
+Always format and lint before committing. Add or update tests if you change behaviour.
 
 ## Submitting changes