- Add POST /create-terminal endpoint with MAX_TERMINALS=5 limit
- Server creates PTY, runs command, registers and broadcasts atomically
- Frontend startTerminal() calls server first, connects in reconnect mode
- Remove registerTerminalOnServer() — server handles registration
- Separate broadcast-only WS clients from PTY clients (no phantom "main" PTY)
- All broadcast functions use broadcastToAll() helper
- Fix resume existing flow to create terminal with --resume flag