feat(chat): Implement end-to-end encrypted swarm messaging system

- Add Swarm Chat documentation with architecture, API endpoints, and security considerations
- Create database schema for chat conversations, messages, and typing indicators
- Implement chat API endpoints for sending, receiving, and managing messages
- Add client-side encryption utilities using RSA-OAEP with SHA-256
- Create chat page UI for viewing conversations and messages
- Add chat type definitions for TypeScript support
- Update database schema with new chat tables and relationships
- Update sidebar navigation to include chat link
- Enable true end-to-end encrypted messaging across swarm nodes without ActivityPub limitations

src/lib/swarm/chat-crypto.ts

@@ -0,0 +1,83 @@
+/**
+ * Swarm Chat Cryptography
+ * 
+ * End-to-end encryption for chat messages using public key cryptography.
+ */
+
+import crypto from 'crypto';
+
+/**
+ * Encrypt a message using the recipient's public key
+ */
+export function encryptMessage(message: string, recipientPublicKey: string): string {
+  try {
+    // Use RSA-OAEP for encryption
+    const encrypted = crypto.publicEncrypt(
+      {
+        key: recipientPublicKey,
+        padding: crypto.constants.RSA_PKCS1_OAEP_PADDING,
+        oaepHash: 'sha256',
+      },
+      Buffer.from(message, 'utf8')
+    );
+    
+    return encrypted.toString('base64');
+  } catch (error) {
+    console.error('Failed to encrypt message:', error);
+    throw new Error('Encryption failed');
+  }
+}
+
+/**
+ * Decrypt a message using the recipient's private key
+ */
+export function decryptMessage(encryptedMessage: string, privateKey: string): string {
+  try {
+    const decrypted = crypto.privateDecrypt(
+      {
+        key: privateKey,
+        padding: crypto.constants.RSA_PKCS1_OAEP_PADDING,
+        oaepHash: 'sha256',
+      },
+      Buffer.from(encryptedMessage, 'base64')
+    );
+    
+    return decrypted.toString('utf8');
+  } catch (error) {
+    console.error('Failed to decrypt message:', error);
+    throw new Error('Decryption failed');
+  }
+}
+
+/**
+ * Sign a message payload for authenticity verification
+ */
+export function signPayload(payload: string, privateKey: string): string {
+  try {
+    const sign = crypto.createSign('SHA256');
+    sign.update(payload);
+    sign.end();
+    
+    const signature = sign.sign(privateKey, 'base64');
+    return signature;
+  } catch (error) {
+    console.error('Failed to sign payload:', error);
+    throw new Error('Signing failed');
+  }
+}
+
+/**
+ * Verify a signed payload
+ */
+export function verifySignature(payload: string, signature: string, publicKey: string): boolean {
+  try {
+    const verify = crypto.createVerify('SHA256');
+    verify.update(payload);
+    verify.end();
+    
+    return verify.verify(publicKey, signature, 'base64');
+  } catch (error) {
+    console.error('Failed to verify signature:', error);
+    return false;
+  }
+}

src/lib/swarm/chat-types.ts

@@ -0,0 +1,66 @@
+/**
+ * Swarm Chat Types
+ * 
+ * Type definitions for the swarm chat system.
+ */
+
+export interface SwarmChatMessage {
+  id: string;
+  conversationId: string;
+  senderHandle: string;
+  senderDisplayName?: string;
+  senderAvatarUrl?: string;
+  senderNodeDomain?: string;
+  encryptedContent: string;
+  deliveredAt?: string;
+  readAt?: string;
+  createdAt: string;
+}
+
+export interface SwarmChatConversation {
+  id: string;
+  type: 'direct' | 'group';
+  participant1Id: string;
+  participant2Handle: string;
+  lastMessageAt?: string;
+  lastMessagePreview?: string;
+  unreadCount?: number;
+  createdAt: string;
+  updatedAt: string;
+}
+
+/**
+ * Payload for sending a chat message to a remote node
+ */
+export interface SwarmChatMessagePayload {
+  messageId: string;
+  senderHandle: string;
+  senderDisplayName?: string;
+  senderAvatarUrl?: string;
+  senderNodeDomain: string;
+  recipientHandle: string;
+  encryptedContent: string;
+  timestamp: string;
+  signature?: string;
+}
+
+/**
+ * Payload for typing indicator
+ */
+export interface SwarmChatTypingPayload {
+  senderHandle: string;
+  senderNodeDomain: string;
+  recipientHandle: string;
+  isTyping: boolean;
+  timestamp: string;
+}
+
+/**
+ * Payload for read receipt
+ */
+export interface SwarmChatReadReceiptPayload {
+  messageId: string;
+  readerHandle: string;
+  readerNodeDomain: string;
+  timestamp: string;
+}