feat(chat): Implement client-side end-to-end encryption with key management

- Add chat keys API endpoint for storing and retrieving encrypted RSA public/private key pairs
- Create client-side crypto utilities for E2E encryption/decryption with hybrid encryption support
- Implement useChatEncryption hook for managing encryption state and key generation in chat UI
- Add chatPublicKey and chatPrivateKeyEncrypted fields to user schema for key storage
- Update chat messages API to return encrypted content with sender's public key for decryption
- Modify send message endpoint to accept pre-encrypted content from client while maintaining legacy server-side encryption
- Update chat page UI to integrate client-side encryption workflow
- Ensure private keys are encrypted client-side with user password before transmission to server
- Server cannot decrypt message content in E2E mode, providing true end-to-end encryption

src/app/api/users/[handle]/route.ts

@@ -94,7 +94,8 @@ export async function GET(request: Request, context: RouteContext) {
             website: user.website,
             movedTo: user.movedTo,
             isBot: user.isBot,
-            publicKey: user.publicKey, // Needed for E2E encrypted chat
+            publicKey: user.publicKey, // RSA key for signing
+            chatPublicKey: user.chatPublicKey, // ECDH key for E2E chat
         };
         
         // If this is a bot, include owner info