feat: twitch integration, event system and CI/CD pipeline

[webbertakken]

Summary

• Twitch OAuth — browser-based auth flow with token persistence, automatic refresh, and Helix API client
• EventSub + IRC — real-time follow/subscribe events via WebSocket, chat presence and send via IRC
• Widgets — chat presence, follow events, event log, and enhanced chat/settings widgets with drag-to-reposition persistence
• Event bus + file logger — centralised event system with local log file storage
• CI/CD pipeline — Release Please for automatic versioning via conventional commits, cross-platform Tauri builds (Windows x64, Linux x64, Linux arm64, macOS x64, macOS arm64), PR title linting, and workflow file linting

Test plan

• Verify OAuth flow completes and tokens persist across restarts
• Verify EventSub receives follow events and displays in widget
• Verify chat widget sends and receives messages
• Verify widget positions persist after drag
• Verify CI workflows trigger correctly on push to main / tag / PR