feat(stats): add Hide Kana filter and fix vocabulary exclusion matching

- Remove overlay mining image toast; OSD card notifications no longer flash a frame screenshot
- Add Hide Kana toggle to frequency rank table to filter kana-only headwords
- Fix vocab exclusions to deduplicate and match token variants (e.g. ない / 無い) under one exclusion entry
- Skip cover image fetching when the overview tab is inactive

stats/src/lib/cover-images.ts

@@ -22,6 +22,14 @@ export function getCoverImageKey(kind: CoverImageKind, id: number): string {
   return `${kind}:${id}`;
 }
 
+export function buildCoverImageRequestKey(
+  animeIds: number[],
+  videoIds: number[],
+  refreshToken = 0,
+): string {
+  return `a:${animeIds.join(',')}|m:${videoIds.join(',')}|r:${refreshToken}`;
+}
+
 export function collectSessionCoverRequests(
   sessions: Pick<SessionSummary, 'animeId' | 'videoId'>[],
 ): CoverImageRequest {