Add persistent NotebookLM session manager

[PlacidusaxAlarak]

Summary

• add a persistent session_manager.py daemon/client for NotebookLM conversations
• keep ask_question.py backward-compatible while adding optional --session-id
• persist serializable session metadata in data/sessions.json
• document lifecycle commands and update cleanup coverage

What changed

• add background session daemon that owns long-lived Playwright + BrowserContext + Page
• map each session_id to a reusable BrowserSession
• support create, ask, list, info, reset, close, and gc
• serialize session metadata only; do not attempt to serialize Playwright runtime objects
• preserve stateless behavior as the default path

Validation

• python3 -m py_compile scripts/*.py
• validated auth flow under proxy
• locally exercised create, two consecutive ask calls, list, info, reset, close, and gc
• validated ask_question.py --session-id ... forwarding into the persistent session manager

Notes

• session persistence is process-bound; daemon restarts do not restore live Playwright objects
• Linux testing used explicit browser proxy configuration for NotebookLM access