TerminalManager was trying to create an asyncio task at module import time,
but no event loop exists yet during import. This caused RuntimeError on startup.
Changes:
- _start_idle_check() now checks if event loop is running before creating task
- If no loop exists, silently skips (will be started lazily)
- Added lazy start call in get_or_create_session() when websocket connects
- Terminal sessions now persist across WebSocket disconnections
- Added circular output buffer (10KB) for replay on reconnect
- Added idle timeout cleanup (30 minutes)
- Added reset functionality via WebSocket message and HTTP endpoint
- Concurrent connections close old WebSocket when new one connects
- Frontend: Added reset button with confirmation dialog
- Frontend: Handle resetting status and reconnection
Refs: persistent-terminal-sessions