feat(topbar): the recording lives in the pill — green pulse, REC clock, Stop Recording

Build 730 (creator):

- Left pill while recording: solid #2ECC71 dot pulsing 1.0 <-> 0.2 on the existing one-second timer, and
  "REC: hh:mm:ss" in Consolas so the digits cannot jitter the pill's width. Idle face unchanged.
- Right pill while recording: a stop square and "Stop Recording"; clicking it runs the normal stop, which
  halts and resets the clock and returns the pair to "Local MP4" / "Start Recording".
- The separate reality line (dot + REC/LIVE + elapsed + End) is now LIVE-ONLY: a recording would otherwise
  print the same three facts twice. RunningVisible is IsLive, and ShowOutputStage no longer hides itself
  for a recording (it must be on screen to carry the clock and the stop).

Two rules collided and are now separated rather than merged: a creator's Stop on a recording restores the
Local MP4 pair (build 730), while a pipeline FAILURE still clears both pills (the 2026-09-01 zombie rule).
StopStream(afterFailure:) carries the difference, and the pump-failure path passes it.

RealAppHost.Run was rethrowing with `throw failure;`, which destroyed the original stack — a failing
assertion inside the action reported the wrapper's line instead of its own. ExceptionDispatchInfo now
preserves it; that is how the two failures above were located in one pass instead of five.

680 pass (one audio-pipe instance flake under full-suite load, passes alone), 0 warnings.
Scope justification: Assets/starting-background.jpg is outside this unit — the creator's replacement art,
still awaiting their visual check.

ytLive.Tests/TopBarWorldTests.cs

@@ -63,6 +63,19 @@ public class TopBarWorldTests
             Assert.True(vm.LocalMp4ChipVisible);
             Assert.True(vm.ShowStartRecordingAction);
             Assert.False(vm.ShowEndRecordingAction);
+            Assert.Equal("Local MP4", vm.RecordChipText);
+
+            // Recording: the pill carries REC + the clock, the stage stays up, and the live reality
+            // line does not (its dot/elapsed/stop would be a second set of the same facts).
+            vm.IsRecording = true;
+            Assert.True(vm.ShowOutputStage);
+            Assert.False(vm.RunningVisible);
+            Assert.False(vm.ShowStartRecordingAction);
+            Assert.True(vm.ShowEndRecordingAction);
+            Assert.StartsWith("REC: ", vm.RecordChipText);
+
+            vm.IsRecording = false;
+            Assert.Equal("Local MP4", vm.RecordChipText);
 
             // Neither action exists while building scenes.
             vm.EnterBuildWorldCommand.Execute(null);