feat(analytics): add optional Aptabase event tracking UI

Integrate Aptabase analytics via a Tauri plugin and add a privacy
notice flow plus a settings dialog to control whether anonymous
usage events are sent. The app now tracks key user actions while
ensuring analytics never blocks core Git operations.

- Add analytics tracking helper and Aptabase plugin wiring
- Persist analytics consent in localStorage and gate tracking
- Introduce notice and settings dialogs, plus new event calls

src/lib/components/RepoLoadingOverlay.svelte

@@ -43,7 +43,10 @@
 <style>
   .repo-loading {
     position: fixed;
-    inset: 0;
+    top: var(--app-titlebar-height, 42px);
+    right: 0;
+    bottom: 0;
+    left: 0;
     z-index: 400;
     display: grid;
     place-items: center;