refactor: remove temp files, compiled output, and hardcoded NotebookLM logic from extension

- Delete findings.md, progress.md, task_plan.md (development artifacts)
- Delete extension/dist/background.js (compiled output, should not be in source)
- Replace hardcoded NotebookLM workspace/URL classification in extension with
  generic domain/path matching stored in session bind criteria. The extension
  is infrastructure — site-specific logic belongs in adapters, not here.
  handleBindCurrent now stores matchDomain/matchPathPrefix in the session,
  and maybeBindWorkspaceToExistingTab uses those stored criteria instead of
  checking for 'site:notebooklm' or 'notebooklm.google.com' directly.

Author: jackwener