Restores all features dropped when merging main into dev:
- Keyboard shortcuts (send, dictation-confirm) with full e2e chain
- Feature toggles (plan/fast mode) in agent status bar
- Sidebar kebab menu (Remove Project) on project rows
- Combined model selector (sticky header, sizing, favorites sort, search)
- Question form Enter key submit with guard
- Input focus restoration (composer + AgentStatusBar onDropdownClose)
- Draft-agent feature toggles and focus restoration
- Provider diagnostics UI (settings section, diagnostic sheet, status badge)
- Provider diagnostics server (snapshot manager, diagnostic utils, RPC)
Fixes dev-branch regressions:
- New workspace button now opens composer in setup dialog via beginWorkspaceSetup
- Setup tab auto-opens when workspace setup is running
