- Defined `hopgate_stream.proto` with message definitions for stream-based DTLS tunneling, including `Request`, `Response`, `StreamOpen`, `StreamData`, `StreamAck`, and `StreamClose`.
- Added `Envelope` container for top-level message encapsulation.
- Integrated Protobuf code generation into the `Makefile` using `protoc` with `protoc-gen-go`.
- Generated Go types under `internal/protocol/pb`.
- Implemented custom HTML templates for `400`, `404`, `500`, and `525` error pages with multilingual support.
- Added embedded file system for error page templates and assets.
- Introduced fallback mechanism to serve minimal plain text for missing error templates.
- Integrated TailwindCSS for styling error pages, with a build script in `package.json`.
