test(gates): sequence the two-client remote-shadow gate with harness signals

Imported from the codex worktree's uncommitted work
(C:/Users/erikn/.codex/worktrees/bd98/acdream on
codex/atmospheric-rendering-campaign), on top of its 8b7b601b.

The remote-player shadow gate ran two clients on fixed sleeps, so the
observer could move before the primary had taken its 'before' screenshot,
or the primary could take its 'after' shot before the observer had moved.
Now the harness publishes named signal files into each client's artifact
directory and the routes block on them:

- IRetailUiAutomationRuntime.TryIsAutomationSignalPublished, implemented
  by WorldLifecycleAutomationController over <artifactDir>/signals/
  <name>.signal (names validated by AutomationArtifactName, so no path
  escape).
- 'wait signal <name> [timeoutMs]' in RetailUiAutomationScriptRunner.
- run-connected-render-pack-remote-player-gate.ps1 publishes
  'primary-before' to the observer after the primary's before-shot
  completes, then 'observer-moved' to the primary after the observer's
  remote-observer-moved checkpoint.
- Both routes teleport with an explicit heading and wait 12 s to settle.

Build green; the three touched App test classes pass 58/58 including the
two new signal tests.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/AcDream.App.Tests/Diagnostics/ConnectedRenderPackGateContractTests.cs

@@ -250,6 +250,8 @@ Remove-ConnectedGraphicalSessionConfig -State $state -Path $sessionConfigPath
         Assert.Contains("[int]$classes.RemotePlayers -lt 1", source, StringComparison.Ordinal);
         Assert.Contains("live: session failed:", source, StringComparison.Ordinal);
         Assert.Contains("DistinctAccountsConfigured", source, StringComparison.Ordinal);
+        Assert.Contains("Publish-ClientSignal $observerRoot 'primary-before'", source, StringComparison.Ordinal);
+        Assert.Contains("Publish-ClientSignal $primaryRoot 'observer-moved'", source, StringComparison.Ordinal);
         Assert.Contains("both clients entered world with the same character identity", source, StringComparison.Ordinal);
         Assert.Contains("Restore-ConnectedRenderPackGateEnvironment $primaryState", source, StringComparison.Ordinal);
         Assert.Contains("Restore-ConnectedRenderPackGateEnvironment $observerState", source, StringComparison.Ordinal);
@@ -267,9 +269,11 @@ Remove-ConnectedGraphicalSessionConfig -State $state -Path $sessionConfigPath
             observer,
             "command /teleloc 0x09040008",
             "wait materialized 1 90000",
+            "checkpoint remote-observer-ready",
+            "wait signal primary-before 120000",
             "input down MovementForward",
             "input up MovementForward",
-            "checkpoint remote-observer");
+            "checkpoint remote-observer-moved");
 
         string primary = ReadTool("connected-render-pack-remote-primary.route.txt");
         AssertAppearsInOrder(
@@ -277,6 +281,7 @@ Remove-ConnectedGraphicalSessionConfig -State $state -Path $sessionConfigPath
             "command /teleloc 0x09040008",
             "wait materialized 1 90000",
             "screenshot remote-player-before 15000",
+            "wait signal observer-moved 120000",
             "screenshot remote-player-after 15000",
             "checkpoint remote-primary");
     }