docs: add terminal API and user documentation

- Add docs/api/terminal.md with WebSocket protocol and reset endpoint
- Add docs/features/terminal.md with user guide for persistent sessions
- Add docs/features/terminal-troubleshooting.md with diagnostic steps
- Mark tasks 8.1-8.3 complete

Refs: persistent-terminal-sessions tasks 8.x

docs/features/terminal.md

@@ -0,0 +1,83 @@
+# Terminal Sessions
+
+Terminal sessions provide interactive shell access to your running tool instances directly in the browser.
+
+## Persistent Sessions
+
+Terminal sessions are **persistent** - they survive browser refreshes, network interruptions, and tab switches.
+
+### How It Works
+
+- When you open a terminal, a shell session starts inside the tool instance container
+- If you close the browser or lose connection, the session keeps running
+- When you reconnect, you reattach to the same session with all previous output preserved
+- Sessions automatically clean up after 30 minutes of inactivity
+
+### Reconnecting
+
+If your connection drops:
+1. The terminal shows "Reconnecting..." status
+2. The client automatically attempts to reconnect with exponential backoff
+3. On successful reconnection, buffered output is replayed
+4. You can continue working where you left off
+
+## Resetting the Terminal
+
+If your terminal becomes unresponsive or you want a fresh start:
+
+1. Click the **Reset** button in the terminal header
+2. Confirm the reset action
+3. The current shell is killed and a new one starts
+4. All terminal history is cleared
+
+**Note:** Resetting only affects the terminal session, not the tool instance itself. Any files you've created remain intact.
+
+## Mobile Terminal
+
+On mobile devices, the terminal includes:
+- Special keys panel (Ctrl, Alt, Tab, arrows, etc.)
+- Font size controls
+- Auto-hiding header for maximum screen space
+- Touch-friendly interface
+
+## Keyboard Shortcuts
+
+Standard terminal shortcuts work as expected:
+- `Ctrl+C`: Send interrupt signal
+- `Ctrl+D`: Send EOF (close shell if empty)
+- `Ctrl+L`: Clear screen
+- `Ctrl+Z`: Suspend process
+
+Special keys can be accessed via the special keys panel on mobile or by using modifier combinations.
+
+## Troubleshooting
+
+### Connection Issues
+
+**"Connection closed" error:**
+- The tool instance may have stopped - check the instance status
+- Network issues - the client will auto-reconnect
+- Session timeout - sessions expire after 30 minutes of inactivity
+
+**Terminal not responding:**
+- Try resetting the terminal using the Reset button
+- Check if the tool instance is still running
+- Refresh the page to force reconnection
+
+### Display Issues
+
+**Text not visible:**
+- Adjust font size using +/- buttons
+- Check if the terminal has focus (click inside it)
+- Try resizing the browser window
+
+**Characters not appearing:**
+- Ensure the terminal has focus
+- Check if a modifier key is stuck (Ctrl, Alt)
+- Reset the terminal if stuck
+
+## Session Limits
+
+- **One connection per terminal:** Only one browser tab can connect to a terminal session at a time. Opening a new connection closes the old one.
+- **30-minute idle timeout:** Sessions without activity are automatically cleaned up
+- **Buffer size:** Up to 10KB of output is buffered for replay on reconnection