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>

lib/tab-bar-insets.ts

@@ -50,6 +50,17 @@ export function useFloatingActionBottom(): number {
   return tabBar + homeIndicator + spacing.xs;
 }
 
+/**
+ * Bottom padding for tab-root ScrollViews (Dashboard, Invoices, etc.).
+ * Uses full tab-bar clearance — do not trim; undershooting hides content under the bar.
+ */
+export function useTabScreenScrollPadding(): number {
+  const { bottom: homeIndicator } = useSafeAreaInsets();
+  const tabBar = useNativeTabBarHeight();
+
+  return tabBar + homeIndicator + spacing.sm;
+}
+
 /** @deprecated Use useTabBarScrollPadding */
 export function useTabBarInset() {
   return useTabBarScrollPadding();