Add remote key fetch proxy and improve chat reliability

Introduces an API route to proxy remote key bundle fetches, improving CORS handling for secure chat. Updates chat UI to handle error states and retries, enhances key/identity synchronization, and refactors message sending to support remote node domains. Also adds CORS preflight support to the .well-known chat route and improves in-memory key store management.

src/app/chat/page.tsx

@@ -258,14 +258,27 @@ export default function ChatPage() {
             // conversation.participant2 might have valid handle.
             // We resolve DID first.
             let did = selectedConversation.participant2.did;
+            // We need to support nodeDomain for existing chats too.
+            // But Conversation interface might lack it.
+            // We can try to resolve it from handle if needed, or if we stored it?
+            // "participant2" comes from API.
+            // Let's assume we re-fetch to be safe if it's remote?
+            // Or just check handle structure?
+            let nodeDomain = undefined;
+            if (selectedConversation.participant2.handle.includes('@')) {
+                const parts = selectedConversation.participant2.handle.split('@');
+                if (parts.length === 2) nodeDomain = parts[1];
+            }
+
             if (!did) {
                 const res = await fetch(`/api/users/${encodeURIComponent(selectedConversation.participant2.handle)}`);
                 const data = await res.json();
                 did = data.user?.did;
+                nodeDomain = data.user?.nodeDomain || nodeDomain; // API is authoritative
                 if (!did) throw new Error('User not found');
             }
 
-            await sendMessage(did, newMessage);
+            await sendMessage(did, newMessage, nodeDomain);
 
             // Legacy UI expects message reload.
             setNewMessage('');
@@ -293,15 +306,20 @@ export default function ChatPage() {
             }
 
             // Send "Hello" to init session
-            await sendMessage(data.user.did, '👋');
+            await sendMessage(data.user.did, '👋', data.user.nodeDomain);
 
             setShowNewChat(false);
             setNewChatHandle('');
             loadConversations(false);
             // Select the new conversation (we might need to find it)
             // For now just reload list.
-        } catch (e) {
-            alert('Failed to start chat');
+        } catch (e: any) {
+            console.error('Start chat failed:', e);
+            if (e.message.includes('Recipient keys not found')) {
+                alert('This user has not set up secure chat yet. They need to log in to enable end-to-end encryption.');
+            } else {
+                alert('Failed to start chat: ' + e.message);
+            }
         } finally { setSending(false); }
     };
 
@@ -351,8 +369,27 @@ export default function ChatPage() {
         );
     }
 
+    // Error State
+    if (status === 'error') {
+        return (
+            <div style={{ display: 'flex', flexDirection: 'column', height: '100vh', alignItems: 'center', justifyContent: 'center', gap: '16px' }}>
+                <Shield size={48} style={{ color: 'var(--destructive)' }} />
+                <h2 style={{ fontSize: '20px', fontWeight: 600 }}>Connection Failed</h2>
+                <p style={{ color: 'var(--foreground-secondary)', maxWidth: '300px', textAlign: 'center' }}>
+                    Unable to initialize secure chat. This might be a network issue or missing keys.
+                </p>
+                <button
+                    onClick={() => ensureReady('RETRY', user?.id || 'retry')}
+                    className="btn btn-primary"
+                >
+                    Retry Connection
+                </button>
+            </div>
+        );
+    }
+
     // Loading State
-    if (status === 'initializing' || status === 'generating_keys') {
+    if ((!isReady && status !== 'error') || status === 'initializing' || status === 'generating_keys') {
         return (
             <div style={{ display: 'flex', flexDirection: 'column', height: '100vh', alignItems: 'center', justifyContent: 'center' }}>
                 <Loader2 className="animate-spin" size={32} />