feat(stats): add sentence search tab and fix mining card behavior

- Add Search tab with realtime subtitle sentence search, media context, and mining actions
- Persist library card size selection across reloads
- Fix selection text written only for sentence cards, not word/audio cards
- Fix word mining audio routed to SentenceAudio field when present
- Fix sentence card created immediately before slow media generation completes
- Fix Anki config resolved at request time for sentence mining
- Prefer non-Signs/Songs tracks when auto-selecting secondary subtitle language

stats/src/lib/sentence-search.tsx

@@ -0,0 +1,84 @@
+import type { ReactNode } from 'react';
+import type { SentenceSearchResult } from '../types/stats';
+
+export interface SentenceMatchRange {
+  start: number;
+  end: number;
+}
+
+export interface SentenceSearchMineAvailability {
+  canMineSentence: boolean;
+  canMineWordAudio: boolean;
+  exactMatch: boolean;
+  unavailableReason: string | null;
+}
+
+function normalizedSearchWord(query: string): string {
+  return query.trim();
+}
+
+export function findExactSentenceMatches(text: string, query: string): SentenceMatchRange[] {
+  const needle = normalizedSearchWord(query);
+  if (!needle) return [];
+
+  const ranges: SentenceMatchRange[] = [];
+  const haystack = text.toLocaleLowerCase();
+  const normalizedNeedle = needle.toLocaleLowerCase();
+  let searchFrom = 0;
+
+  while (searchFrom < haystack.length) {
+    const index = haystack.indexOf(normalizedNeedle, searchFrom);
+    if (index < 0) break;
+    ranges.push({ start: index, end: index + needle.length });
+    searchFrom = index + needle.length;
+  }
+
+  return ranges;
+}
+
+export function getSentenceSearchMineAvailability(
+  result: Pick<SentenceSearchResult, 'sourcePath' | 'segmentStartMs' | 'segmentEndMs' | 'text'>,
+  query: string,
+): SentenceSearchMineAvailability {
+  const exactMatch = findExactSentenceMatches(result.text, query).length > 0;
+  const unavailableReason = !result.sourcePath
+    ? 'This source has no local file path.'
+    : result.segmentStartMs == null || result.segmentEndMs == null
+      ? 'This line is missing segment timing.'
+      : null;
+
+  return {
+    canMineSentence: unavailableReason === null,
+    canMineWordAudio: unavailableReason === null && exactMatch,
+    exactMatch,
+    unavailableReason,
+  };
+}
+
+export function renderSentenceWithMatches(text: string, query: string): ReactNode {
+  const ranges = findExactSentenceMatches(text, query);
+  if (ranges.length === 0) return text;
+
+  const parts: ReactNode[] = [];
+  let cursor = 0;
+  ranges.forEach((range, index) => {
+    if (range.start > cursor) {
+      parts.push(text.slice(cursor, range.start));
+    }
+    parts.push(
+      <mark
+        key={`${range.start}-${index}`}
+        className="rounded bg-ctp-yellow/15 px-0.5 text-ctp-yellow underline decoration-ctp-yellow/60 underline-offset-2"
+      >
+        {text.slice(range.start, range.end)}
+      </mark>,
+    );
+    cursor = range.end;
+  });
+
+  if (cursor < text.length) {
+    parts.push(text.slice(cursor));
+  }
+
+  return parts;
+}