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.

.gitignore

@@ -0,0 +1,14 @@
+# Go
+bin/
+*.test
+*.out
+
+# Local runtime data
+backend/static/uploads/*
+!backend/static/uploads/.gitkeep
+
+# Environment overrides
+.env
+.env.*
+!.env.example
+scripts/env/dev.env