feat(frontend): avatar upload QOL — feedback, re-crop, drop, progress, history

Task 12 batch around the existing crop/preview flow:
- Success Notice (auto-dismiss ~2.5s) after an avatar upload.
- "Reposition" re-crops the current avatar without re-picking a file.
- Drag & drop an image straight onto the profile avatar circle.
- Real upload progress via a new XHR-backed api.upload (fetch has none);
  refreshOnce now also stores the renewed token (reload-restore fix).
- Local avatar history (last 5, IndexedDB, this-device-only) strip that
  re-uploads a stored crop. Stored as ArrayBuffer (Blob is not cloneable
  under structuredClone); label makes the per-device scope explicit.
- Added a "success" tone to Notice.

Infra (same session): registered @shared/@features/@pages/@app/@test path
aliases in vite.config + tsconfigs and rewrote deep ../../../ imports;
moved avatar components into components/avatar/ to keep folders at <=4 files.

Tests: avatarHistory cap/order, recrop visibility, drop-opens-cropper,
client upload/progress/401-retry. bun test 103 pass, lint 0 errors, build ok.

frontend/src/app/App.tsx

@@ -1,7 +1,7 @@
 import { QueryClient, QueryClientProvider } from '@tanstack/react-query'
 import { createBrowserRouter, RouterProvider } from 'react-router'
-import { SessionProvider } from '../features/auth/session'
-import { ActiveThemeProvider } from '../features/themes/useActiveTheme'
+import { SessionProvider } from '@features/auth/session'
+import { ActiveThemeProvider } from '@features/themes/useActiveTheme'
 import { routes } from './routes'
 
 const queryClient = new QueryClient({