Enable parallel UI test execution via per-session data isolation

Each test class now gets a unique session ID (UUID) passed to the app
via UI_TEST_SESSION_ID environment variable. The app uses this to:

- Route GroupUserDefaults to a session-specific UserDefaults suite,
  preventing tests from clobbering each other's AppStorage state
- Create an in-memory SwiftData container instead of the shared
  on-disk App Group store, eliminating SQLite contention

Refactored 8 test classes that bypassed BaseUITestCase.setUp() with
custom launch args — they now use overridable `localeArguments` and
`extraLaunchArguments` properties, keeping session ID injection
centralized. Added `relaunchApp(resetState:bypassSubscription:)` to
BaseUITestCase for tests that need mid-test relaunch with different
subscription state.

Includes a ParallelUITests.xctestplan with class-level parallelism
enabled and random execution ordering.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Reflect.xcodeproj/xcshareddata/xcschemes/ParallelUITests.xctestplan

@@ -0,0 +1,26 @@
+{
+  "configurations" : [
+    {
+      "id" : "9A1B2C3D-4E5F-6A7B-8C9D-0E1F2A3B4C5D",
+      "name" : "Parallel UI Tests",
+      "options" : {
+        "testExecutionOrdering" : "random"
+      }
+    }
+  ],
+  "defaultOptions" : {
+    "maximumTestExecutionTimeAllowance" : 180,
+    "testTimeoutsEnabled" : true
+  },
+  "testTargets" : [
+    {
+      "parallelizable" : true,
+      "target" : {
+        "containerPath" : "container:Reflect.xcodeproj",
+        "identifier" : "Tests iOS",
+        "name" : "Tests iOS"
+      }
+    }
+  ],
+  "version" : 1
+}