feat: add JSON-RPC documentation generator

- Implemented a new Go program in `mods/server/docgen/main.go` to generate documentation for JSON-RPC methods registered in the server.
- The generator parses the server code, extracts method signatures, and formats them into a Markdown document.
- Added a directive in `mods/server/generate.go` to run the documentation generator using `go generate`.

Author: OutOfBedlam