Fix UI test failures: registration dismiss cascade, onboarding reset, test stability

- Fix registration flow dismiss cascade: chain fullScreenCover → sheet onDismiss
  so auth state is set only after all UIKit presentations are removed, preventing
  RootView from swapping LoginView→MainTabView behind a stale sheet
- Fix onboarding reset: set hasCompletedOnboarding directly instead of calling
  completeOnboarding() which has an auth guard that fails after DataManager.clear()
- Stabilize Suite1 registration tests, Suite6 task tests, Suite7 contractor tests
- Add clean-slate-per-suite via AuthenticatedUITestCase reset state
- Improve test account seeding and screen object reliability

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

iosApp/HoneyDueUITests/Framework/AuthenticatedUITestCase.swift

@@ -15,8 +15,6 @@ class AuthenticatedUITestCase: BaseUITestCase {
         ("admin", "test1234")
     }
 
-    override var includeResetStateLaunchArgument: Bool { false }
-
     // MARK: - API Session
 
     private(set) var session: TestSession!
@@ -24,11 +22,21 @@ class AuthenticatedUITestCase: BaseUITestCase {
 
     // MARK: - Lifecycle
 
+    override class func setUp() {
+        super.setUp()
+        guard TestAccountAPIClient.isBackendReachable() else { return }
+        // Ensure both known test accounts exist (covers all subclass credential overrides)
+        if TestAccountAPIClient.login(username: "testuser", password: "TestPass123!") == nil {
+            _ = TestAccountAPIClient.createVerifiedAccount(username: "testuser", email: "testuser@honeydue.com", password: "TestPass123!")
+        }
+        if TestAccountAPIClient.login(username: "admin", password: "test1234") == nil {
+            _ = TestAccountAPIClient.createVerifiedAccount(username: "admin", email: "admin@honeydue.com", password: "test1234")
+        }
+    }
+
     override func setUpWithError() throws {
-        if needsAPISession {
-            guard TestAccountAPIClient.isBackendReachable() else {
-                throw XCTSkip("Backend not reachable at \(TestAccountAPIClient.baseURL)")
-            }
+        guard TestAccountAPIClient.isBackendReachable() else {
+            throw XCTSkip("Backend not reachable at \(TestAccountAPIClient.baseURL)")
         }
 
         try super.setUpWithError()