Close all 25 codex audit findings across KMP, iOS, and Android

Remediate all P0-S priority findings from cross-platform architecture audit:
- Harden token storage with EncryptedSharedPreferences (Android) and Keychain (iOS)
- Add SSL pinning and certificate validation to API clients
- Fix subscription cache race conditions and add thread-safe access
- Add input validation for document uploads and file type restrictions
- Refactor DocumentApi to use proper multipart upload flow
- Add rate limiting awareness and retry logic to API layer
- Harden subscription tier enforcement in SubscriptionHelper
- Add biometric prompt for sensitive actions (Login, Onboarding)
- Fix notification permission handling and device registration
- Add UI test infrastructure (page objects, fixtures, smoke tests)
- Add CI workflow for mobile builds

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

iosApp/CaseraUITests/PageObjects/MainTabScreen.swift

@@ -0,0 +1,88 @@
+import XCTest
+
+/// Page object for the main tab view that appears after login.
+///
+/// Provides navigation to each tab (Residences, Tasks, Contractors, Documents, Profile)
+/// and a logout flow. Uses predicate-based element lookup to match the existing test patterns.
+class MainTabScreen: BaseScreen {
+
+    // MARK: - Tab Elements
+
+    var residencesTab: XCUIElement {
+        app.tabBars.buttons.containing(NSPredicate(format: "label CONTAINS[c] 'Residences'")).firstMatch
+    }
+
+    var tasksTab: XCUIElement {
+        app.tabBars.buttons.containing(NSPredicate(format: "label CONTAINS[c] 'Tasks'")).firstMatch
+    }
+
+    var contractorsTab: XCUIElement {
+        app.tabBars.buttons.containing(NSPredicate(format: "label CONTAINS[c] 'Contractors'")).firstMatch
+    }
+
+    var documentsTab: XCUIElement {
+        app.tabBars.buttons.containing(NSPredicate(format: "label CONTAINS[c] 'Documents'")).firstMatch
+    }
+
+    var profileTab: XCUIElement {
+        app.tabBars.buttons.containing(NSPredicate(format: "label CONTAINS[c] 'Profile'")).firstMatch
+    }
+
+    override var isDisplayed: Bool {
+        residencesTab.waitForExistence(timeout: timeout)
+    }
+
+    // MARK: - Navigation
+
+    @discardableResult
+    func goToResidences() -> Self {
+        waitForElement(residencesTab).tap()
+        return self
+    }
+
+    @discardableResult
+    func goToTasks() -> Self {
+        waitForElement(tasksTab).tap()
+        return self
+    }
+
+    @discardableResult
+    func goToContractors() -> Self {
+        waitForElement(contractorsTab).tap()
+        return self
+    }
+
+    @discardableResult
+    func goToDocuments() -> Self {
+        waitForElement(documentsTab).tap()
+        return self
+    }
+
+    @discardableResult
+    func goToProfile() -> Self {
+        waitForElement(profileTab).tap()
+        return self
+    }
+
+    // MARK: - Logout
+
+    /// Logs out by navigating to the Profile tab and tapping the logout button.
+    /// Handles the confirmation alert automatically.
+    func logout() {
+        goToProfile()
+
+        let logoutButton = app.buttons[AccessibilityIdentifiers.Profile.logoutButton]
+        if logoutButton.waitForExistence(timeout: 5) {
+            waitForHittable(logoutButton).tap()
+
+            // Handle confirmation alert
+            let alert = app.alerts.firstMatch
+            if alert.waitForExistence(timeout: 3) {
+                let confirmLogout = alert.buttons["Log Out"]
+                if confirmLogout.exists {
+                    confirmLogout.tap()
+                }
+            }
+        }
+    }
+}