feat: add PTY/terminal session support to Process Manager API

Add Docker-style terminal support with -t (TTY) and -i (interactive) flags:

Backend (Rust):
- Add portable-pty dependency for PTY allocation on Unix
- Extend StartProcessRequest with tty, interactive, and terminalSize options
- Add PTY process spawning with TERM=xterm-256color
- Add WebSocket endpoint for bidirectional terminal I/O
- Add terminal resize endpoint (POST /process/:id/resize)
- Add terminal input endpoint (POST /process/:id/input)
- Support base64-encoded binary input
- Process info now includes tty, interactive, and terminalSize fields
- Terminal output is logged to combined.log for persistence

Frontend (Inspector UI):
- Add @xterm/xterm and addons for terminal rendering
- Create Terminal component with xterm.js integration
- Add tabbed view (Terminal/Logs) for PTY processes
- Terminal auto-connects via WebSocket when process is expanded
- Support terminal resize with ResizeObserver
- Show PTY badge on processes with TTY enabled
- Graceful handling of process exit and disconnection

API:
- GET /v1/process/:id/terminal - WebSocket for terminal I/O
- POST /v1/process/:id/resize - Resize terminal (cols, rows)
- POST /v1/process/:id/input - Write data to terminal

WebSocket protocol:
- type: 'data' - Terminal output (server -> client)
- type: 'input' - Terminal input (client -> server)
- type: 'resize' - Resize request (client -> server)
- type: 'exit' - Process exited (server -> client)
- type: 'error' - Error message (server -> client)

docs/process-terminal.md

@@ -0,0 +1,155 @@
+# Process Terminal Support
+
+This document describes the PTY/terminal session support added to the Process Manager API.
+
+## Overview
+
+The Process Manager now supports Docker-style terminal sessions with `-t` (TTY) and `-i` (interactive) flags. When a process is started with TTY enabled, a pseudo-terminal (PTY) is allocated, allowing full interactive terminal applications to run.
+
+## API
+
+### Starting a Process with TTY
+
+```bash
+curl -X POST http://localhost:2468/v1/process \
+  -H "Content-Type: application/json" \
+  -d '{
+    "command": "bash",
+    "args": [],
+    "tty": true,
+    "interactive": true,
+    "terminalSize": {
+      "cols": 120,
+      "rows": 40
+    }
+  }'
+```
+
+Response includes `tty: true` and `interactive: true` flags.
+
+### Terminal WebSocket
+
+Connect to a running PTY process via WebSocket:
+
+```
+ws://localhost:2468/v1/process/{id}/terminal
+```
+
+#### Message Types
+
+**Client -> Server:**
+- `{"type": "input", "data": "ls -la\n"}` - Send keyboard input
+- `{"type": "resize", "cols": 120, "rows": 40}` - Resize terminal
+
+**Server -> Client:**
+- `{"type": "data", "data": "..."}` - Terminal output
+- `{"type": "exit", "code": 0}` - Process exited
+- `{"type": "error", "message": "..."}` - Error occurred
+
+### Terminal Resize
+
+```bash
+curl -X POST http://localhost:2468/v1/process/{id}/resize \
+  -H "Content-Type: application/json" \
+  -d '{"cols": 120, "rows": 40}'
+```
+
+### Terminal Input (REST)
+
+For non-WebSocket clients:
+
+```bash
+curl -X POST http://localhost:2468/v1/process/{id}/input \
+  -H "Content-Type: application/json" \
+  -d '{"data": "ls -la\n"}'
+```
+
+For binary data, use base64 encoding:
+
+```bash
+curl -X POST http://localhost:2468/v1/process/{id}/input \
+  -H "Content-Type: application/json" \
+  -d '{"data": "bHMgLWxhCg==", "base64": true}'
+```
+
+## Inspector UI
+
+The Inspector UI now shows:
+- PTY badge on processes with TTY enabled
+- Terminal/Logs tabs for PTY processes
+- Interactive xterm.js terminal when expanded
+- Auto-resize on window/container resize
+
+## Testing
+
+### Start the Server
+
+```bash
+cargo run --package sandbox-agent -- serve
+```
+
+### Test Interactive Bash
+
+```bash
+# Start a bash shell with PTY
+curl -X POST http://localhost:2468/v1/process \
+  -H "Content-Type: application/json" \
+  -d '{
+    "command": "bash",
+    "tty": true,
+    "interactive": true
+  }'
+
+# Open the Inspector UI and interact with the terminal
+open http://localhost:2468
+```
+
+### Test with vim
+
+```bash
+curl -X POST http://localhost:2468/v1/process \
+  -H "Content-Type: application/json" \
+  -d '{
+    "command": "vim",
+    "args": ["test.txt"],
+    "tty": true,
+    "interactive": true
+  }'
+```
+
+### Test with htop
+
+```bash
+curl -X POST http://localhost:2468/v1/process \
+  -H "Content-Type: application/json" \
+  -d '{
+    "command": "htop",
+    "tty": true,
+    "interactive": true
+  }'
+```
+
+## Implementation Details
+
+### Backend
+
+- Uses `portable-pty` crate for cross-platform PTY support (Unix only for now)
+- PTY output is continuously read and broadcast to WebSocket subscribers
+- PTY input is received via channel and written to the master PTY
+- Terminal resize uses `TIOCSWINSZ` ioctl via portable-pty
+- `TERM=xterm-256color` is set automatically
+
+### Frontend
+
+- Uses `@xterm/xterm` for terminal rendering
+- `@xterm/addon-fit` for auto-sizing
+- `@xterm/addon-web-links` for clickable URLs
+- WebSocket connection with JSON protocol
+- ResizeObserver for container size changes
+
+## Limitations
+
+- PTY support is currently Unix-only (Linux, macOS)
+- Windows support would require ConPTY integration
+- Maximum of 256 broadcast subscribers per terminal
+- Terminal output is logged but not line-buffered (raw bytes)