Get Gsc Oauth Url

Return the Google OAuth authorization URL for Search Console.

CLI flow: cli_port is carried in state so the callback redirects back to the CLI. Web flow: origin (frontend host) + site_id + the logged-in user_email are signed into state so the callback returns the user to the right site AND attaches the GSC token to THEIR account — even for email/OTP users whose Google (used for the GSC consent) isn't their login. user_email must be HMAC-signed with AGENT_API_KEY (only the frontend, which holds that key, can vouch for a logged-in identity).