fix app lock hanging on macOS and blocking the photo picker

- Lock only when the scene really backgrounds: transient inactive
  states (system photo picker, app switcher) no longer swap in the
  lock screen and break gallery selection on iOS.
- Cache biometric availability once per session off the main thread
  instead of calling LAContext.canEvaluatePolicy in view bodies,
  which froze the macOS lock screen, and auto-prompt biometrics on
  iOS only.
- Keep UI tests as an opt-in target and guard both fixes in
  verify.sh.

Luma.xcodeproj/xcshareddata/xcschemes/Luma.xcscheme

@@ -64,17 +64,6 @@
                ReferencedContainer = "container:Luma.xcodeproj">
             </BuildableReference>
          </TestableReference>
-         <TestableReference
-            skipped = "NO"
-            parallelizable = "NO">
-            <BuildableReference
-               BuildableIdentifier = "primary"
-               BlueprintIdentifier = "A086B6D25E7969CB643F1C8A"
-               BuildableName = "LumaUITests.xctest"
-               BlueprintName = "LumaUITests"
-               ReferencedContainer = "container:Luma.xcodeproj">
-            </BuildableReference>
-         </TestableReference>
       </Testables>
       <CommandLineArguments>
       </CommandLineArguments>