fix(chat/post): PostCard-Bilder-Ecken, Chat-Spinner-Hänger, Bild-Cache

- PostCard: Bilder mit borderRadius 10 + overflow:hidden — Ecken wieder rund
- dm.tsx: myUserId synchron aus useAuthStore statt async getSession —
  behebt den hängenden Lade-Spinner beim Zurück aus einer Conversation
  (async getSession-Fenster auf jedem Mount → enabled-Flackern der Query)
- ChatBubble: expo-image memory-disk-Cache + 200ms-Transition für
  smootheres Bild-Laden

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

apps/rebreak-native/app/dm.tsx

@@ -16,13 +16,13 @@ import { Ionicons } from '@expo/vector-icons';
 import { useQuery, useQueryClient } from '@tanstack/react-query';
 import { useTranslation } from 'react-i18next';
 import { apiFetch } from '../lib/api';
-import { supabase } from '../lib/supabase';
 import { ChatBubble, type ChatMsg } from '../components/chat/ChatBubble';
 import { ChatInput, type SendPayload } from '../components/chat/ChatInput';
 import { DmChatBackground } from '../components/chat/DmChatBackground';
 import { useDmRealtime } from '../hooks/useChatRealtime';
 import { useColors } from '../lib/theme';
 import { useThemeStore } from '../stores/theme';
+import { useAuthStore } from '../stores/auth';
 import { UserAvatar } from '../components/UserAvatar';
 import { ChatHeaderStatus } from '../components/chat/ChatHeaderStatus';
 
@@ -60,7 +60,7 @@ export default function DmScreen() {
   const styles = makeStyles(colors);
   const queryClient = useQueryClient();
   const flatRef = useRef<FlatList>(null);
-  const [myUserId, setMyUserId] = useState<string | undefined>(undefined);
+  const myUserId = useAuthStore((s) => s.user?.id);
 
   const colorScheme = useThemeStore((s) => s.colorScheme);
   const chatBg = colorScheme === 'dark' ? '#1a1f1e' : '#EDE8E1';
@@ -95,13 +95,6 @@ export default function DmScreen() {
     setReplyTo(null);
   }, [userId]);
 
-  // Lade meine User-ID
-  useEffect(() => {
-    supabase.auth.getSession().then(({ data }) => {
-      setMyUserId(data.session?.user.id);
-    });
-  }, []);
-
   // Lade DM-History — staleTime:0 erzwingt immer frischen Fetch (kein Cache-Hit-Bug)
   const { isLoading, isFetching } = useQuery({
     queryKey: ['dm-history', userId],

apps/rebreak-native/components/PostCard.tsx

@@ -315,8 +315,8 @@ function PostCardImpl({ post, onCommentPress }: Props) {
               setImageAspectRatio(Math.max(0.6, Math.min(1.78, ratio)));
             }
           }}
-          className="w-full rounded-xl mt-3"
-          style={{ aspectRatio: imageAspectRatio ?? 1.78 }}
+          className="w-full mt-3"
+          style={{ aspectRatio: imageAspectRatio ?? 1.78, borderRadius: 10, overflow: 'hidden' }}
           contentFit="cover"
         />
       )}

apps/rebreak-native/components/chat/ChatBubble.tsx

@@ -199,6 +199,8 @@ export function ChatBubble({
                   source={{ uri: msg.attachmentUrl }}
                   style={styles.image}
                   contentFit="cover"
+                  cachePolicy="memory-disk"
+                  transition={200}
                 />
                 {isImageOnly && (
                   <View style={styles.imageTimeOverlay}>