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.

ViewModels/MainViewModel.Streaming.cs

@@ -191,7 +191,7 @@ public partial class MainViewModel : ViewModelBase
     /// <summary>Creator ruling 2026-10-30: EDIT decides whether the ON-AIR start is the real
     /// livestream or the test one, which is why the separate TEST button is gone.</summary>
     public SessionStartKind PrimaryStartKind =>
-        SessionStartDecision.For(RecordPillOn, OnAirPillOn, EditingActive);
+        SessionStartDecision.For(RecordPillOn, OnAirPillOn);
 
     public string PrimaryStartButtonLabel => SessionStartDecision.LabelFor(PrimaryStartKind);
 
@@ -229,7 +229,7 @@ public partial class MainViewModel : ViewModelBase
     public string EndButtonText =>
         IsRecording && !IsLive ? "Stop Recording"
         : IsTestStream ? "End Test"
-        : "End Stream";
+        : "End Live Stream";
 
     /// <summary>TASK 41 — Test is a child of Stream (creator ruling: "Test should only
     /// proc when we've selected stream"): a dry-run of the livestream, so it exists