Add Google account emoji pairing for Google Messages

[Phloraxx]

Summary

Updates the optional Google Messages/libgm connector to match the current upstream pairing flow.

Primary flow

• Google-account/Gaia pairing
• accepts the upstream-required Google cookie set from cookie JSON, a raw Cookie: header, or a browser DevTools Copy-as-cURL request
• filters input down to only the seven cookie names upstream uses
• fetches Messages Web config, starts Gaia pairing, displays the derived emoji, waits for the phone response, persists the completed AuthData, then reconnects
• keeps account/pairing state visible only to authenticated operator views

Fallback

• retains QR pairing and automatic refresh under explicit /pair/qr routes
• preserves the original QR endpoints as backward-compatible aliases

Safety/lifecycle

• cookie values are never logged or echoed
• failed/incomplete pairing is not persisted
• valid Google-account sessions require the complete required cookie set
• concurrent Google/QR pairing attempts are rejected
• in-progress pairing cancellation does not call the remote-unpair RPC intended for completed sessions
• connector remains read-only and payment verification remains independent of libgm

Validation

• frontend npm ci, audit, typecheck and production build passed
• uncached Go suite passed
• race detector passed
• go vet passed
• staticcheck passed
• govulncheck reports no reachable vulnerabilities
• clean production Docker build passed
• production-shaped container with GMESSAGES_ENABLED=true starts healthy/unpaired

Live phone emoji confirmation remains the final device acceptance test after deployment.