Complete re-validation remediation: KMP architecture, iOS platform, XCUITest rewrite

Phases 1-6 of fixes.md — closes all 13 issues from codex_issues_2.md re-validation:

KMP Architecture:
- Fix subscription purchase/restore response contract (VerificationResponse aligned)
- Add feature benefits auth token + APILayer init flow
- Remove ResidenceFormScreen direct API bypass (use APILayer)
- Wire paywall purchase/restore to real SubscriptionApi calls

iOS Platform:
- Add iOS Keychain token storage via Swift KeychainHelper
- Implement Google Sign-In via ASWebAuthenticationSession (GoogleSignInManager)
- DocumentViewModelWrapper observes DataManager for auto-updates
- Add missing accessibility identifiers (document, task columns, Google Sign-In)

XCUITest Rewrite:
- Rewrite test infrastructure: zero sleep() calls, accessibility ID lookups
- Create AuthCriticalPathTests and NavigationCriticalPathTests
- Delete 14 legacy brittle test files (Suite0-10, templates)
- Fix CaseraTests module import (@testable import Casera)

All platforms build clean. TEST BUILD SUCCEEDED.

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

composeApp/src/androidMain/kotlin/com/example/casera/platform/PlatformUpgradeScreen.android.kt

@@ -0,0 +1,57 @@
+package com.example.casera.platform
+
+import android.app.Activity
+import androidx.compose.runtime.*
+import androidx.compose.ui.platform.LocalContext
+import com.example.casera.ui.subscription.UpgradeScreen
+import kotlinx.coroutines.launch
+
+@Composable
+actual fun PlatformUpgradeScreen(
+    onNavigateBack: () -> Unit,
+    onSubscriptionChanged: () -> Unit
+) {
+    val context = LocalContext.current
+    val activity = context as? Activity
+    val billingManager = remember { BillingManager.getInstance(context) }
+    val scope = rememberCoroutineScope()
+
+    // Load products on launch
+    LaunchedEffect(Unit) {
+        billingManager.startConnection(
+            onSuccess = {
+                scope.launch { billingManager.loadProducts() }
+            }
+        )
+    }
+
+    // Watch for successful purchase
+    val purchasedProductIDs by billingManager.purchasedProductIDs.collectAsState()
+    var initialPurchaseCount by remember { mutableStateOf(purchasedProductIDs.size) }
+
+    LaunchedEffect(purchasedProductIDs) {
+        if (purchasedProductIDs.size > initialPurchaseCount) {
+            onSubscriptionChanged()
+            onNavigateBack()
+        }
+    }
+
+    UpgradeScreen(
+        onNavigateBack = onNavigateBack,
+        onPurchase = { planId ->
+            val product = billingManager.getProduct(planId)
+            if (product != null && activity != null) {
+                billingManager.launchPurchaseFlow(activity, product)
+            }
+        },
+        onRestorePurchases = {
+            scope.launch {
+                val restored = billingManager.restorePurchases()
+                if (restored) {
+                    onSubscriptionChanged()
+                    onNavigateBack()
+                }
+            }
+        }
+    )
+}