feat(entitlement): pre-release switch so Release builds can test 60 fps

The frame-rate boundary is correct as a product rule, but it only bites in a
Release build, where DevBuild.IsDevelopment is false and DeveloperMode cannot
unlock anything — exactly the build whose performance numbers are worth reading
(see docs/ai/environment.md: Debug pixel paths are several times slower). 60 fps
could not be tested at all.

OutputProfile.EntitlementEnforced is false: every shipped tier is selectable by
any build, and HasProOutput — the one property the tier setter, the dropdown's
strikethrough and the locked-item style all read — answers yes regardless of
ownership. static readonly rather than const, so the consumed `||` does not fold
into unreachable operand code (same reason as DevBuild.IsDevelopment).

The licence indicator row is suppressed while the switch is off: it exists to
explain what the boundary costs, and claiming "Steam ID Limit: 60fps" to an
unowned build would be a false statement. Docs corrected in place — the enforced
rule is unchanged, only its state is recorded.

Tests: one integration case covers both switch states (unowned build reaches
1080p60 with the switch off, 1080p30 with it on), so flipping at launch leaves no
red test behind. The two suites that anchor on the pinned licence row early-return
while it is absent; EntitlementTests covers that state meanwhile.

667 pass, build 0 warnings.

ViewModels/MainViewModel.Alerts.cs

@@ -50,7 +50,10 @@ public partial class MainViewModel
     private void RefreshSteamLicenceAlert()
     {
         var existing = _attentionAlerts.FirstOrDefault(alert => alert.Id == SteamLicenceAlertId);
-        var hidden = IsAppOwned && _steamLicenceDismissed;
+        // The row exists to explain what the frame-rate boundary costs when it applies. While the
+        // pre-release switch is off nothing is limited, so announcing a limit would be a false claim.
+        var hidden = !OutputProfile.EntitlementEnforced
+                     || (IsAppOwned && _steamLicenceDismissed);
 
         if (hidden)
         {

ViewModels/MainViewModel.OutputProfile.cs

@@ -38,7 +38,13 @@ public partial class MainViewModel
         private set => SetProperty(ref _entitlementErrorMessage, value);
     }
 
-    public bool HasProOutput => DeveloperMode || IsAppOwned;
+    /// <summary>
+    /// May this run emit 60 fps? True while the pre-release switch is off
+    /// (<see cref="OutputProfile.EntitlementEnforced"/>), or for a development build's override, or
+    /// when Steam says the paid app is owned. Everything that gates on the frame rate reads this one
+    /// property: the tier setter, the dropdown's strikethrough, the locked-item style.
+    /// </summary>
+    public bool HasProOutput => !OutputProfile.EntitlementEnforced || DeveloperMode || IsAppOwned;
 
     private static IEntitlement CreateEntitlement()
     {