Timers: heuristically bind LTC when the stage layout omits the field

Verified against ProPresenter 21.4: the legacy stage-display protocol
(ptl 610 — the only version PP21 accepts; newer values get 'out of
date') omits stage objects it predates, so a timecode field labeled LTC
never appears in any layout's frame list, and no timecode messages were
observed while idle. Fallback: an unknown uid streaming timecode-shaped
text (a fourth :FF group; not any configured timer's uuid) is bound as
LTC after two advancing samples, and that binding survives layout
refreshes. pp-timers-mock gains --ltc-unlisted to exercise the path.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tools/pp-timers-mock.js

@@ -46,6 +46,9 @@ const NO_LTC = args.includes('--no-ltc');
 const DROP = new Set(args.flatMap((a) => (a.startsWith('--drop=') ? a.slice(7).split(',') : [])));
 const STAGE_PWD = (args.find((a) => a.startsWith('--stage-pwd=')) || '').slice(12);
 const NO_LTC_FIELD = args.includes('--no-ltc-field');
+// Like real ProPresenter 21: the layout list omits the timecode field, but
+// its updates still stream — exercises the module's heuristic binding.
+const LTC_UNLISTED = args.includes('--ltc-unlisted');
 const FPS = 30;
 
 const startedAt = Date.now();
@@ -164,7 +167,7 @@ const STAGE_LAYOUT = {
   nme: 'Timers',
   fme: [
     { nme: 'Current Slide', typ: 1 },
-    ...(NO_LTC_FIELD ? [] : [{ nme: 'LTC', typ: 7, uid: 'LTC-FIELD' }]),
+    ...(NO_LTC_FIELD || LTC_UNLISTED ? [] : [{ nme: 'LTC', typ: 7, uid: 'LTC-FIELD' }]),
     { nme: 'Sermon Countdown', typ: 7, uid: 'T1-SERMON' },
   ],
 };