refactor(ipc): remove dead preload methods and the ASS line broadcast (#293)

Drop 16 overlay preload methods with no caller (onSubtitleAss,
getCurrentSubtitleAss, onVisibility, getOverlayVisibility,
openYomitanSettings, quitApp, toggleOverlay, getMecabStatus,
setMecabEnabled, getKeybindings, saveControllerPreference,
getAnkiConnectStatus, setAnkiConnectEnabled, clearAnkiConnectHistory,
cycleRuntimeOption, appendClipboardVideoToQueue) along with their
IPC_CHANNELS keys, handlers, validators and dep plumbing.

With both ASS consumers gone, stop observing sub-text/ass in mpv and
remove the subtitle-ass-change event chain and appState.currentSubAssText.
The main-process functions these wrapped stay; tray, CLI, shortcuts and
session actions still use them.

src/core/services/mpv.test.ts

@@ -444,17 +444,6 @@ test('MpvIpcClient reconnect replays property subscriptions and initial state re
       (command as { command: unknown[] }).command[1] === 1 &&
       (command as { command: unknown[] }).command[2] === 'sub-text',
   );
-  const hasAssSubtitleSubscription = commands.some(
-    (command) =>
-      Array.isArray((command as { command: unknown[] }).command) &&
-      (command as { command: unknown[] }).command[0] === 'observe_property' &&
-      (command as { command: unknown[] }).command[2] === 'sub-text/ass',
-  );
-  const hasDeprecatedAssSubtitleProperty = commands.some(
-    (command) =>
-      Array.isArray((command as { command: unknown[] }).command) &&
-      (command as { command: unknown[] }).command.includes('sub-text-ass'),
-  );
   const hasPathRequest = commands.some(
     (command) =>
       Array.isArray((command as { command: unknown[] }).command) &&
@@ -464,8 +453,6 @@ test('MpvIpcClient reconnect replays property subscriptions and initial state re
 
   assert.equal(hasSecondaryVisibilityReset, true);
   assert.equal(hasTrackSubscription, true);
-  assert.equal(hasAssSubtitleSubscription, true);
-  assert.equal(hasDeprecatedAssSubtitleProperty, false);
   assert.equal(hasPathRequest, true);
 });