fix(native): mail-sheet modal-conflict + google-oauth picker + feed-bg contrast

- mail/MailAccountSettingsSheet: handleSaveTitle + handleSavePassword now
  dismiss sheet FIRST, then trigger parent SuccessAlert via setTimeout(350ms).
  Fixes iOS "already presenting" crash + page-freeze when editing mailbox name.
  Also fixes double-click-needed UX bug.
- stores/auth: signOut adds WebBrowser.coolDownAsync() to clear OAuth cookies.
  signInWithOAuth for Google adds prompt=select_account — forces account-picker
  on every sign-in attempt instead of auto-reusing previous account.
- app/(app)/index: feed page uses colors.groupedBg instead of colors.bg —
  matches iOS Mail/Messages list-style, post-cards stand out clearer.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

apps/rebreak-native/app/(app)/index.tsx

@@ -80,7 +80,7 @@ export default function HomeScreen() {
   );
 
   return (
-    <View style={{ flex: 1, backgroundColor: colors.bg }}>
+    <View style={{ flex: 1, backgroundColor: colors.groupedBg }}>
       <AppHeader />
 
       <FlatList

apps/rebreak-native/components/mail/MailAccountSettingsSheet.tsx

@@ -257,8 +257,12 @@ export function MailAccountSettingsSheet({
   async function handleSaveTitle() {
     const ok = await saveTitle(account.id, titleDraft);
     if (ok) {
-      onTitleSaved(titleDraft.trim() || null);
-      setMode('list');
+      const newTitle = titleDraft.trim() || null;
+      // Sheet ZUERST dismissen, dann nach Animation-Complete Parent informieren.
+      // Sonst rendern Sheet (closing) + SuccessAlert (opening) gleichzeitig → iOS
+      // wirft „already presenting"-Crash + Page-Freeze. ~350ms = FormSheet-Dismiss.
+      handleClose();
+      setTimeout(() => onTitleSaved(newTitle), 350);
     }
   }
 
@@ -266,10 +270,10 @@ export function MailAccountSettingsSheet({
     setLocalError(null);
     const result = await connect({ email: account.email, password: passwordDraft });
     if (result.ok) {
-      setPasswordDraft('');
-      setPasswordVisible(false);
-      onPasswordSaved();
-      setMode('list');
+      // Symmetrisch zu handleSaveTitle: Sheet zuerst dismissen, dann nach
+      // Animation-Complete Parent informieren — sonst Modal-Conflict-Crash.
+      handleClose();
+      setTimeout(() => onPasswordSaved(), 350);
     } else {
       setLocalError(result.error ?? t('mail.connect_failed'));
     }

apps/rebreak-native/stores/auth.ts

@@ -73,6 +73,14 @@ export const useAuthStore = create<AuthState>((set) => ({
 
   signOut: async () => {
     await supabase.auth.signOut();
+    // Google-OAuth-Cookie in SafariViewController/Chrome Custom Tabs leeren,
+    // sonst springt der nächste Sign-in stillschweigend auf den vorigen Account
+    // statt den Account-Picker zu zeigen.
+    try {
+      await WebBrowser.coolDownAsync();
+    } catch {
+      // ignore
+    }
     set({ session: null, user: null });
   },
 
@@ -91,6 +99,9 @@ export const useAuthStore = create<AuthState>((set) => ({
       options: {
         redirectTo: redirectUri,
         skipBrowserRedirect: true,
+        // Google: prompt=select_account erzwingt den Account-Picker,
+        // auch wenn der Browser noch eine aktive Google-Session hat.
+        ...(provider === 'google' ? { queryParams: { prompt: 'select_account' } } : {}),
       },
     });