feat: add automated bulk OAuth login via Outlook Web

Add a Python/Playwright script that automates the full ChatGPT OAuth
flow for Outlook-based accounts: enters email, requests a one-time
code, reads it from Outlook inbox, handles consent page, captures
tokens via local HTTP callback server, and writes them to the plugin
store.

Handles Microsoft interstitials (FIDO/passkey, Stay signed in, etc).
Includes credentials template, gitignore for secrets, and full README
documentation.