fix: webcam identity->device key for output frames; top bar always has a Start; light-pill grouping

Take two (2026-09-01) three confirmed defects, all from creator feedback + the
new resolver logging:

1. NO WEBCAM IN OUTPUT: WebcamSceneConfig.WebcamId carries the identity GUID;
   CameraManager keys sessions by DEVICE id — GetLatestFrame(guid) returned null
   forever, the compositor silently dropped the layer while the preview (bitmap
   path) looked fine. The resolver logging added in 8dcaee0 caught it red-handed.
   DeviceKeyForWebcam maps identity->device through the _webcam singleton (identity
   mismatch / unknown ids pass through). Test: WebcamOutputKeyTests.

2. START BUTTON VANISHED AFTER STOP: my pills-clear ruling met the old
   ShowPrimaryStartButton gate (needed IsConnected or a lit REC pill) — signed-out,
   pills-off = blank top bar, no session reachable. Start is now ALWAYS the idle
   face; unarmed Start records (local needs no account — no dead-end no-op); the
   Sign In button folds into Start's context menu ('Sign in to YouTube', shown while
   disconnected) with a dedicated SignInCommand. SessionTeardownTests extended:
   stopped session must leave a reachable Start.

3. TOP BAR ORDER (creator spec): [sign light] REC [pill]  [sign light] ON-AIR [pill]
   — each reality lamp now sits in front of its own intent switch (was: two pills,
   then two orphaned dots). Sign labels keep the shared StatusSignText style.

Tests: WebcamOutputKey, SessionTeardown, FramePump, WebcamMenuGate, GlobalHotkey,
BroadcastPullOut — 14/14 across the six classes, clean build 0 warnings.

ViewModels/MainViewModel.Streaming.Operations.cs

@@ -21,7 +21,15 @@ public partial class MainViewModel : ViewModelBase
         if (IsLive || IsRecording) return;
         var streaming = OnAirPillOn;
         var recording = RecordPillOn;
-        if (!streaming && !recording) return;
+        if (!streaming && !recording)
+        {
+            // Nothing armed = "record something" (local recording needs no account,
+            // 2026-09-01): a Start that silently no-ops is the dead end the design
+            // principle forbids. The pill lights so reality and intent agree.
+            RecordPillOn = true;
+            BeginRecordOnly();
+            return;
+        }
 
         if (!streaming)
         {