Add Authentik sign-in, fix tab scroll insets, and polish multi-account auth.

Mobile app detects SSO per server, supports OAuth sign-in, and preserves saved
sessions when adding accounts. Tab screens get proper chrome layout and tab-bar
clearance with scrollable page headers.

Co-authored-by: Cursor <cursoragent@cursor.com>

contexts/AuthContext.tsx

@@ -1,5 +1,6 @@
 import { expoClient } from "@better-auth/expo/client";
 import { createAuthClient } from "better-auth/react";
+import { genericOAuthClient } from "better-auth/client/plugins";
 import * as SecureStore from "expo-secure-store";
 import {
   createContext,
@@ -10,6 +11,20 @@ import {
 
 type AuthClient = ReturnType<typeof createAuthClient>;
 
+function createAppAuthClient(apiUrl: string, storagePrefix: string): AuthClient {
+  return createAuthClient({
+    baseURL: apiUrl,
+    plugins: [
+      expoClient({
+        scheme: "beenvoice",
+        storagePrefix,
+        storage: SecureStore,
+      }),
+      genericOAuthClient(),
+    ],
+  });
+}
+
 const AuthContext = createContext<AuthClient | null>(null);
 
 export function AuthProvider({
@@ -22,17 +37,7 @@ export function AuthProvider({
   children: ReactNode;
 }) {
   const client = useMemo(
-    () =>
-      createAuthClient({
-        baseURL: apiUrl,
-        plugins: [
-          expoClient({
-            scheme: "beenvoice",
-            storagePrefix,
-            storage: SecureStore,
-          }),
-        ],
-      }),
+    () => createAppAuthClient(apiUrl, storagePrefix),
     [apiUrl, storagePrefix],
   );