feat(app): GUI backlog — splitter, drag-reorder, fit, persist, modal focus

- LayoutEngine: fix splitter resize (track pointer 1:1 via delta-from-start)
  and add panel drag-to-reorder using raw pointer events with drop indicators
- TerminalView: auto-fit xterm to container via FitAddon + ResizeObserver
- App/TopBar: toggleable sidebar; persist sidebar/events collapse in
  localStorage; bell icon opens the activity log
- Wizard: new-workspace modal now grabs focus and handles keyboard
- deps: add @xterm/addon-fit

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/package.json

@@ -13,6 +13,7 @@
     "@fontsource/inter": "^5.2.8",
     "@tauri-apps/api": "^2",
     "@tauri-apps/plugin-notification": "^2",
+    "@xterm/addon-fit": "^0.10.0",
     "@xterm/addon-search": "^0.16.0",
     "@xterm/addon-webgl": "^0.18.0",
     "@xterm/xterm": "^5.5.0",