feat(topbar): the action follows the armed output; Test is an explicit ask again

Unit C (creator ruling 2026-11-12).

- Local MP4: one button, "Start Recording".
- YouTube: "Private Test Stream" beside "Review & Go Live", the latter with the primary face because it
  is the default ask.
- Running: "End Live Stream" (or "End Test" for a test run, "Stop Recording" for a local one).

The behavioural change underneath: SessionStartDecision.For no longer takes `editing`. Since 2026-10-30
EDIT silently chose test-vs-real, which meant the same button did two different things depending on a
toggle three inches away. With Test as its own button that inference has no job, so For() now reads only
the armed output and ON-AIR always means the real livestream. That supersedes the 2026-10-30 ruling;
SessionStartDecisionTests is rewritten to pin the new matrix rather than the old one.

A signed-out press still starts the sign-in flow instead of sitting dead (no-dead-ends), unchanged from
before — now stated in one place, the two new commands, instead of inside a route table.

680 pass, 0 warnings. Scope justification: Assets/starting-background.jpg is outside this unit — the
creator's replacement art, still awaiting their visual check.

ytLive.Tests/UiShellTests.cs

@@ -49,6 +49,11 @@ public class UiShellTests
         Assert.Contains("IsChecked=\"{Binding OnAirPillOn}\"", topBar);
         Assert.Contains("IsChecked=\"{Binding RecordPillOn}\"", topBar);
 
+        // 2d. The action follows the armed output, and Test is an explicit ask again.
+        Assert.Contains("Content=\"Start Recording\"", topBar);
+        Assert.Contains("Content=\"Private Test Stream\"", topBar);
+        Assert.Contains("Content=\"Review & Go Live\"", topBar);
+
         // 3. Active scene = orange; live stays red.
         Assert.Contains("IsStaged}\" Value=\"True\">\n                                        <Setter Property=\"BorderBrush\" Value=\"{StaticResource Brush.Attention}\"/>", strip);