feat(native/chat): partner avatars + pill-shape search field

- DmItem now goes through resolveAvatar(partnerAvatar, partnerName) so
  the Dicebear-initials fallback kicks in for null avatars, hero ids
  resolve to their image url, and direct URLs pass through. Adds the
  PostCard-style avatarLoadFailed state for graceful broken-image
  fallback.
- Search row pill-shaped (borderRadius 999) with 16px horizontal padding
  and the outline search icon for better visual rhythm.

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

@@ -1,4 +1,4 @@
-import { useState, useCallback } from 'react';
+import { useState, useCallback, useEffect } from 'react';
 import {
   View,
   Text,
@@ -15,6 +15,7 @@ import { Ionicons } from '@expo/vector-icons';
 import { useQuery } from '@tanstack/react-query';
 import { useTranslation } from 'react-i18next';
 import { apiFetch } from '../../lib/api';
+import { resolveAvatar } from '../../lib/resolveAvatar';
 import { AppHeader } from '../../components/AppHeader';
 import { useColors } from '../../lib/theme';
 
@@ -42,16 +43,23 @@ function DmItem({ conv, onPress }: { conv: DmConversation; onPress: () => void }
   const styles = makeStyles(colors);
   const hasUnread = conv.unreadCount > 0;
 
+  const avatarUrl = resolveAvatar(conv.partnerAvatar, conv.partnerName);
+  const [avatarLoadFailed, setAvatarLoadFailed] = useState(false);
+  useEffect(() => { setAvatarLoadFailed(false); }, [avatarUrl]);
+  const avatarInitials = (conv.partnerName.slice(0, 2)).toUpperCase() || '?';
+
   return (
     <TouchableOpacity onPress={onPress} activeOpacity={0.7}>
       <View style={styles.dmRow}>
         <View style={styles.dmAvatar}>
-          {conv.partnerAvatar ? (
-            <Image source={{ uri: conv.partnerAvatar }} style={styles.dmAvatarImg} />
+          {!avatarLoadFailed ? (
+            <Image
+              source={{ uri: avatarUrl }}
+              style={styles.dmAvatarImg}
+              onError={() => setAvatarLoadFailed(true)}
+            />
           ) : (
-            <Text style={styles.dmAvatarInitials}>
-              {conv.partnerName.slice(0, 2).toUpperCase()}
-            </Text>
+            <Text style={styles.dmAvatarInitials}>{avatarInitials}</Text>
           )}
         </View>
         <View style={styles.dmInfo}>
@@ -130,7 +138,7 @@ export default function ChatScreen() {
       {/* Search header */}
       <View style={styles.headerSection}>
         <View style={styles.searchRow}>
-          <Ionicons name="search" size={16} color={colors.textMuted} style={styles.searchIcon} />
+          <Ionicons name="search-outline" size={16} color={colors.textMuted} style={styles.searchIcon} />
           <TextInput
             style={styles.searchInput}
             value={search}
@@ -194,11 +202,11 @@ function makeStyles(colors: ReturnType<typeof useColors>) {
       flexDirection: 'row',
       alignItems: 'center',
       backgroundColor: colors.surfaceElevated,
-      borderRadius: 10,
-      paddingHorizontal: 10,
+      borderRadius: 999,
+      paddingHorizontal: 16,
       paddingVertical: 8,
     },
-    searchIcon: { marginRight: 7 },
+    searchIcon: { marginRight: 8 },
     searchInput: {
       flex: 1,
       fontSize: 14,