Timers: LTC is listener-only; admin switch, device/channel, grouped settings

Simplify LTC to its one working source — the built-in audio listener — and
make the admin UI reflect it.

Module:
- Remove the stage-display websocket source (stage-ws.js, stagePassword)
  and the /v1/timecode/status API probe — both dead on ProPresenter 21.4.
- Remove the remote-reader ingest (POST /ltc, ingestToken, tools/
  ltc-reader.js): the module owns LTC end to end now. The decoder selftest
  moves to modules/propresenter-timers/ltc.selftest.js so the engine stays
  covered.
- composeLtc collapses to the listener: running/stopped/nosignal, or a
  clear note when disabled / no device / capture failed / starting.
- Manifest: ltcEnabled is now a `switch`; ltcDevice and ltcChannel carry
  showWhen:"ltcEnabled"; ProPresenter and LTC fields carry `group` labels.

Shell (admin) — backward-compatible additions, coordinate with the shell lane:
- New `switch` field type (boolean shown as the enable-toggle control).
- `group`: consecutive fields render under a labeled subsection.
- `showWhen: "<key>"`: a field is shown only while that boolean/switch is
  on (and actually collapses — .field[hidden] override, since .field's
  display:flex outranks the [hidden] UA default).
- applyConfigPatch coerces `switch` as boolean. Documented in MODULE-GUIDE.

Verified: engine selftest (29 checks); listener decodes BlackHole loopback
(running 30fps, ageMs); device picker lists inputs; POST /ltc now 404s;
admin shows two labeled groups, the switch, and device/channel appearing
only when the switch is on (computed display none↔flex confirmed).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

modules/propresenter-timers/client.js

@@ -262,9 +262,8 @@ export default function create({ root, moduleApi }) {
 
   function updateLtcAnchor() {
     const l = state?.ltc;
-    // Only the audio sources are extrapolatable — they know the frame rate.
-    const live = l && l.status === 'running' && l.fps > 0
-      && (l.source === 'listener' || l.source === 'reader');
+    // The listener is extrapolatable — it knows the frame rate.
+    const live = l && l.status === 'running' && l.fps > 0 && l.source === 'listener';
     const tc = live ? parseTc(l.time) : null;
     if (!tc) {
       ltcAnchor = null;
@@ -323,14 +322,9 @@ export default function create({ root, moduleApi }) {
     if (ltc.supported === false) {
       mode = 'unavailable';
       card.timeEl.textContent = '—';
-      // The server says why when it knows (stage password rejected, no
-      // stage field labeled LTC, reader offline, …) — surface that over
-      // the generic line.
-      card.stateEl.textContent = ltc.note || 'Timecode not available on this ProPresenter';
-    } else if (ltc.supported === null) {
-      mode = 'waiting';
-      card.timeEl.textContent = displayTime(ltc.time);
-      card.stateEl.textContent = 'Waiting for ProPresenter…';
+      // The server says why when it knows (listener disabled, no device
+      // selected, capture failed, starting up…) — surface that.
+      card.stateEl.textContent = ltc.note || 'LTC not available';
     } else if (ltc.receiving) {
       mode = 'receiving';
       // With an anchor active, paint the frame it implies for now (this
@@ -350,10 +344,9 @@ export default function create({ root, moduleApi }) {
       card.timeEl.textContent = '—';
       card.stateEl.textContent = 'No signal';
     }
-    // The built-in listener and the remote reader are independent of
-    // ProPresenter, so their card must not gray out with the rest when
-    // only ProPresenter is unreachable.
-    const live = ltc.source === 'reader' || ltc.source === 'listener' ? ' src-reader' : '';
+    // The built-in listener is independent of ProPresenter, so its card
+    // must not gray out with the rest when only ProPresenter is unreachable.
+    const live = ltc.source === 'listener' ? ' src-reader' : '';
     card.el.className = `tm-card tm-card-ltc is-ltc-${mode}${live}`;
   }
 
@@ -377,7 +370,7 @@ export default function create({ root, moduleApi }) {
     }
     if (!state.enabled) {
       bannerEl.hidden = true;
-      // The LTC listener/reader feed us with or without ProPresenter — an
+      // The LTC listener feeds us with or without ProPresenter — an
       // LTC-only setup is working, not broken.
       if (state.ltc?.supported) moduleApi.setStatus('ok', 'LTC only — no ProPresenter host configured');
       else moduleApi.setStatus('error', 'No ProPresenter host configured — set one in Admin');