perf: instant proxy mode switching via optimistic UI update

fix: update checker shows correct status + version display + dark mode fixes

feat: proxy pool add form with separate protocol/host/port/auth fields

fix: proxy pool review fixes — security, validation, robustness

feat: add proxy pool for per-account proxy routing

feat: GitHub Star badge + check-for-updates in dashboard header

fix: collapsible model dropdown, default to gpt-5.4, remove legacy gpt-5

feat: add gpt-5.4 + codex-spark support, matrix model selector, extended reasoning efforts

refactor: extract startServer() + path abstraction for Electron reuse