feat: xterm.js + node-pty architecture for Claude CLI web terminal

Complete rewrite from tmux + JSONL parsing to a clean PTY-based approach.
The proxy spawns Claude CLI in a pseudo-terminal via node-pty and relays
terminal I/O as binary WebSocket frames to the simple-chat backend,
which forwards them to the browser where xterm.js renders a full terminal.

- node-pty PTY manager with 50KB replay buffer per session
- Binary frame protocol with chatId multiplexing
- WebSocket client with auto-reconnection and heartbeat
- Directory listing and session listing for the web UI
- README with setup instructions

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/connection/protocol.ts

@@ -0,0 +1,108 @@
+// === WebSocket Protocol Types (xterm.js + node-pty) ===
+
+// Binary frame header for terminal data multiplexing:
+// [1 byte direction][36 bytes chatId ASCII][...payload]
+// Direction: 0x01 = PTY output (proxy→backend→frontend)
+//            0x02 = user input (frontend→backend→proxy)
+export const DIR_PTY_OUTPUT = 0x01;
+export const DIR_USER_INPUT = 0x02;
+export const CHAT_ID_LENGTH = 36; // UUID length
+
+export function encodeBinaryFrame(direction: number, chatId: string, data: Buffer): Buffer {
+  const header = Buffer.alloc(1 + CHAT_ID_LENGTH);
+  header[0] = direction;
+  header.write(chatId, 1, CHAT_ID_LENGTH, 'ascii');
+  return Buffer.concat([header, data]);
+}
+
+export function decodeBinaryFrame(frame: Buffer): { direction: number; chatId: string; data: Buffer } {
+  const direction = frame[0];
+  const chatId = frame.subarray(1, 1 + CHAT_ID_LENGTH).toString('ascii');
+  const data = frame.subarray(1 + CHAT_ID_LENGTH);
+  return { direction, chatId, data };
+}
+
+// JSON control messages
+
+export type BackendMessageType =
+  | 'sync_state'
+  | 'create_pty'
+  | 'kill_pty'
+  | 'resize'
+  | 'list_directories'
+  | 'list_sessions';
+
+export type ProxyMessageType =
+  | 'pty_ready'
+  | 'pty_closed'
+  | 'directories'
+  | 'sessions_list'
+  | 'error';
+
+export type WsMessageType = BackendMessageType | ProxyMessageType;
+
+export interface WsMessage {
+  type: WsMessageType;
+  requestId?: string;
+  payload: unknown;
+}
+
+// === Payload types ===
+
+export interface SyncStatePayload {
+  chats: AgentChatInfo[];
+}
+
+export interface AgentChatInfo {
+  id: string;
+  workDir: string | null;
+  sessionId: string | null;
+  cols?: number;
+  rows?: number;
+}
+
+export interface CreatePtyPayload {
+  chatId: string;
+  dir: string;
+  resumeSessionId?: string;
+  cols: number;
+  rows: number;
+}
+
+export interface KillPtyPayload {
+  chatId: string;
+}
+
+export interface ResizePayload {
+  chatId: string;
+  cols: number;
+  rows: number;
+}
+
+export interface PtyReadyPayload {
+  chatId: string;
+}
+
+export interface PtyClosedPayload {
+  chatId: string;
+  exitCode: number;
+}
+
+export interface ListDirectoriesPayload {
+  path: string;
+}
+
+export interface DirectoryEntry {
+  name: string;
+  isDirectory: boolean;
+}
+
+export interface DirectoriesPayload {
+  requestId: string;
+  entries: DirectoryEntry[];
+}
+
+export interface ErrorPayload {
+  chatId?: string;
+  message: string;
+}