docs: add RoadRaven to Apps Built with Electrobun

RoadRaven is a local-first desktop app for building and live-monitoring visual roadmap trees, where Claude Code and other MCP hosts update node status over a localhost WebSocket as they work. It ships on Electrobun 2.x with Cottontail as the main-process runtime, CEF on Linux and WebView2 on Windows, with installers for both Windows and Linux.