feat: add Gmail receipts and travel connector

[yeziR4]

Summary

• add an experimental Gmail Playwright connector for purchase receipts and travel confirmations
• search Gmail directly with category:purchases OR flight OR ticket
• support manual Google login and 2FA through the headed browser takeover flow
• export up to 100 messages with id, date, sender, subject, and snippet
• add the gmail.receipts schema, manifest, registry entry, fixture, catalog entries, icon, and release artifact

Validation

• live-tested against an authenticated Gmail session
• confirmed the current Gmail fallback row layout and fixed its date-cell selector
• live result contained all five required non-empty string fields
• strict connector validation: passed
• manifest validation: passed (0 errors, 0 warnings)
• scope schema coverage: passed
• fixture index check: passed
• scope catalog check: passed
• connector index and immutable artifact check: passed

Privacy

Authentication and extraction run locally in the user's browser session. The connector does not request or automate Google credentials.