feat(stats): add library entry deletion and app-wide delete progress

- Add "Delete Entry" to the anime detail view: removes every episode, session, subtitle line, rollup and cover art for a title plus the vocab counts derived from them, then drops it from the Library grid; refused while that title is currently playing.
- Show delete progress (session, session group, episode, entry) app-wide via a top progress bar + status toast that persist across tab switches, detail views, and the stats overlay window instead of going blank off-tab.
- Fix delete and Vocabulary-tab performance: store seen_ms on word/kanji occurrences so deletes subtract only removed rows via a covering index instead of rescanning each word's full history, and paginate vocab rows before aggregating anime counts.
- Migrate existing databases in place on first launch after upgrade.

stats/src/components/overview/OverviewTab.tsx

@@ -6,7 +6,6 @@ import { StreakCalendar } from './StreakCalendar';
 import { RecentSessions } from './RecentSessions';
 import { TrackingSnapshot } from './TrackingSnapshot';
 import { TrendChart } from '../trends/TrendChart';
-import { DeleteProgressToast } from '../common/DeleteProgressToast';
 import { buildOverviewSummary, buildStreakCalendar } from '../../lib/dashboard-data';
 import { apiClient } from '../../lib/api-client';
 import { getStatsClient } from '../../hooks/useStatsApi';
@@ -160,8 +159,6 @@ export function OverviewTab({
         deletingIds={deletingIds}
         isActive={isActive}
       />
-
-      <DeleteProgressToast count={deletingIds.size} />
     </div>
   );
 }