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/middleware/security.go

@@ -0,0 +1,16 @@
+package middleware
+
+import "net/http"
+
+func SecurityHeaders(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		header := w.Header()
+		header.Set("X-Content-Type-Options", "nosniff")
+		header.Set("X-Frame-Options", "DENY")
+		header.Set("Referrer-Policy", "strict-origin-when-cross-origin")
+		header.Set("Permissions-Policy", "camera=(), microphone=(), geolocation=()")
+		header.Set("Content-Security-Policy", "default-src 'self'; img-src 'self' data: blob:; media-src 'self' blob:; font-src 'self'; style-src 'self'; script-src 'self'; base-uri 'self'; frame-ancestors 'none'")
+
+		next.ServeHTTP(w, r)
+	})
+}