feat(anki): add runtime toggle for media timing review

- Add session-only runtime option with live config hot-reload support
- Document the runtime palette toggle

src/config/config.test.ts

@@ -2181,6 +2181,7 @@ test('runtime options registry is centralized', () => {
   const ids = RUNTIME_OPTION_REGISTRY.map((entry) => entry.id);
   assert.deepEqual(ids, [
     'anki.autoUpdateNewCards',
+    'anki.mediaReviewTiming',
     'subtitle.annotation.knownWords.highlightEnabled',
     'subtitle.annotation.knownWords.maturityEnabled',
     'subtitle.annotation.nPlusOne',