fix(subtitles): re-annotate invalidated text during autoplay priming

Autoplay priming called onSubtitleChange after a cache miss, which only asks
whether the text is new. When the miss came from an invalidation (mining a
card while the line is on screen) the text was unchanged, so nothing was
scheduled and the line stayed unannotated for as long as it was displayed.
refreshCurrentSubtitle checks the cache generation as well, so it re-tokenizes
for the new generation; the resume fallback is kept for the case where it
genuinely has nothing to do.

refreshCurrentSubtitle also returned false for empty text while a run was in
flight, even though that run goes on to emit the empty subtitle. It now
reports the pending emit so callers do not release the prefetch pause early.

The priming tests now drive the real subtitle processing controller instead of
a stub. The previous stub encoded the wrong assumption about unchanged text
and so could not catch either bug.

changes/subtitle-tokenization-performance.md

@@ -11,4 +11,5 @@ area: subtitles
 - Fixed a reading that stopped covering its surface when an unmatched kana run extended the preceding token (for example a trailing る on 待ち合わせ), which silently disabled the known-word reading fallback for those tokens.
 - Subtitle prefetching no longer stays paused for the rest of a cue when the same subtitle text is reported twice and there is nothing to tokenize. This covers the startup and overlay priming paths as well as ordinary subtitle changes.
 - Character name and image lookups are now refreshed centrally whenever a character dictionary sync changes its content, so a newly added name can no longer be skipped by a stale candidate list.
+- A subtitle that was on screen when its annotations were invalidated (by mining a card, for example) is now re-annotated instead of staying plain for the rest of the line.
 - Character name annotations no longer cost a dictionary lookup at every position in a line. The scanner now knows which name forms the current title's character dictionary actually contains and only checks where one can start, which removes the whole overhead of having the character dictionary enabled (measured: 21 lookups per line down to 10, the same as with it disabled). Titles with no cached character data keep the previous exhaustive scan, so a missing snapshot costs speed rather than a missing name.