feat: initialize warpbox.dev project structure and backend

Initialize the repository with the core Go backend architecture and a frontend mockup for warpbox.dev, a self-hosted file-sharing application.

- Set up Go backend modules for configuration, HTTP server, middleware, handlers, and templates.
- Add local development scripts, environment templates, and basic project configuration.
- Include a React-based frontend mockup under the docs directory.

backend/libs/handlers/app.go

@@ -0,0 +1,34 @@
+package handlers
+
+import (
+	"log/slog"
+	"net/http"
+
+	"warpbox.dev/backend/libs/config"
+	"warpbox.dev/backend/libs/services"
+	"warpbox.dev/backend/libs/web"
+)
+
+type App struct {
+	cfg           config.Config
+	logger        *slog.Logger
+	renderer      *web.Renderer
+	uploadService *services.UploadService
+}
+
+func NewApp(cfg config.Config, logger *slog.Logger, renderer *web.Renderer, uploadService *services.UploadService) *App {
+	return &App{
+		cfg:           cfg,
+		logger:        logger,
+		renderer:      renderer,
+		uploadService: uploadService,
+	}
+}
+
+func (a *App) RegisterRoutes(mux *http.ServeMux) {
+	mux.HandleFunc("GET /", a.Home)
+	mux.HandleFunc("GET /healthz", a.Health)
+	mux.HandleFunc("GET /api/v1/health", a.Health)
+	mux.HandleFunc("POST /api/v1/upload", a.UploadPlaceholder)
+	mux.Handle("GET /static/", a.Static())
+}