feat: add git integration enhancements (phase 1)

Real-time git awareness:
- Auto-refresh git context on window focus and after run completion
- Periodic background polling (60s interval, configurable via settings)
- Pre-run working tree snapshot capture for project-backed runs
- Debounced refresh scheduling to coalesce rapid triggers

Backend (main process):
- GitService.captureWorkingTreeSnapshot() with per-file metadata
- Enriched parseWorkingTree() producing ProjectGitWorkingTreeFile entries
- AryxAppService: scheduleProjectGitRefresh(), periodic timer, focus hook
- preRunGitSnapshot persisted on SessionRunRecord with normalization

Frontend (renderer):
- Settings toggle for auto-refresh (General > Git section)
- RunTimeline: git baseline indicator showing branch and change summary
- Enhanced GitContextBadge tooltip with change breakdown details
- ChatPane: enriched git tooltip with staged/modified/untracked counts
- New IPC channel: setGitAutoRefreshEnabled

Tests: 8 new tests covering snapshot capture, refresh scheduling,
scratchpad skip behavior, and auto-refresh setting persistence.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/shared/contracts/channels.ts

@@ -17,6 +17,7 @@ export const ipcChannels = {
   setTerminalHeight: 'settings:set-terminal-height',
   setNotificationsEnabled: 'settings:set-notifications-enabled',
   setMinimizeToTray: 'settings:set-minimize-to-tray',
+  setGitAutoRefreshEnabled: 'settings:set-git-auto-refresh-enabled',
   checkForUpdates: 'app:check-for-updates',
   installUpdate: 'app:install-update',
   saveMcpServer: 'tooling:mcp:save',