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>

components/PageHeader.tsx

@@ -1,22 +1,20 @@
 import { StyleSheet, Text, View } from "react-native";
 
-import { fonts, spacing } from "@/constants/theme";
+import { fonts } from "@/constants/theme";
 import { tabLayout } from "@/lib/tab-layout";
 import { useAppTheme } from "@/contexts/ThemeContext";
-import { useTopChromeHeight } from "@/lib/top-chrome-insets";
 
 type PageHeaderProps = {
   title: string;
   subtitle: string;
 };
 
-/** Title block — transparent, scrolls under TopChromeBar blur. */
+/** Title block — scrolls with tab screen content. */
 export function PageHeader({ title, subtitle }: PageHeaderProps) {
   const { colors } = useAppTheme();
-  const topChromeHeight = useTopChromeHeight();
 
   return (
-    <View style={[tabLayout.pageHeader, { paddingTop: topChromeHeight + spacing.md }]}>
+    <View style={tabLayout.pageHeader}>
       <Text style={[styles.title, { color: colors.foreground }]}>{title}</Text>
       <Text style={[styles.subtitle, { color: colors.mutedForeground }]}>{subtitle}</Text>
     </View>