fix(subtitles): release prefetch pause across all priming paths

The repeated-subtitle pause leak was only fixed for ordinary subtitle
changes. Startup autoplay priming and visible-overlay priming pause the same
way and also ignored whether any tokenization was scheduled, so a cache miss
on text the controller already holds (mining a card while the line is on
screen) left prefetching idle for the rest of the cue.

Pause and release are now one operation via pausePrefetchUntilEmit, and both
controller entry points report whether an emit is expected. A repeat arriving
while a run is already in flight keeps the pause, since that run still emits.

Also invalidate the character dictionary lookups centrally from the sync
completion handler instead of at three manager call sites. Ordinary selection
sync never invalidated them, so a stale non-null name candidate list could
skip a newly added name for up to five seconds; a missing list falls back to
the exhaustive scan, but a stale one does not. Ordering matters: the
invalidation runs before the subtitle refreshes so they re-tokenize against
the new dictionary content.

Docs: subtitle-overlay-priming no longer claims every subtitle change calls
onSeek().

src/core/services/subtitle-processing-controller.ts

@@ -23,7 +23,8 @@ export interface SubtitleProcessingController {
    * gate work on the emit (such as pausing subtitle prefetching) need to know.
    */
   onSubtitleChange: (text: string) => boolean;
-  refreshCurrentSubtitle: (textOverride?: string) => void;
+  /** Same contract as onSubtitleChange: whether an emit is expected. */
+  refreshCurrentSubtitle: (textOverride?: string) => boolean;
   invalidateTokenizationCache: () => void;
   preCacheTokenization: (text: string, data: SubtitleData) => void;
   consumeCachedSubtitle: (text: string) => SubtitleData | null;
@@ -176,7 +177,8 @@ export function createSubtitleProcessingController(
   return {
     onSubtitleChange: (text: string) => {
       if (text === latestText) {
-        return false;
+        // A run already in flight for this text will still emit for it.
+        return processing;
       }
       latestText = text;
       if (
@@ -195,15 +197,16 @@ export function createSubtitleProcessingController(
         latestText = textOverride;
       }
       if (!latestText.trim()) {
-        return;
+        return false;
       }
-      if (
-        processing ||
-        (latestText === lastEmittedText && cacheGeneration === lastEmittedGeneration)
-      ) {
-        return;
+      if (processing) {
+        return true;
+      }
+      if (latestText === lastEmittedText && cacheGeneration === lastEmittedGeneration) {
+        return false;
       }
       processLatest();
+      return true;
     },
     invalidateTokenizationCache: () => {
       tokenizationCache.clear();