feat(auth): allow configurable redirect URI in remote/manual OAuth flow

[salmonumbrella]

Summary

• add --redirect-uri to gog auth add for manual/remote OAuth flows
• thread redirect override through googleauth.AuthorizeOptions
• use redirect override for remote step 1 URL generation and manual/code exchange when needed
• preserve state validation behavior and add tests for override/reuse/precedence/invalid input

Testing

• go test ./internal/googleauth ./internal/cmd
• go test ./...

Closes #356