[FEATURE]: Snowflake Cortex SSO (external browser) authentication #31702

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

The Snowflake Cortex provider currently only supports PAT authentication. On Snowflake accounts that use an external identity provider (Okta, Entra ID, etc.) users can't easily generate a PAT and would prefer browser-based SSO.

Request: support Snowflake's external-browser (SSO) login for the snowflake-cortex provider, using the same handshake the official Snowflake drivers use (authenticator-request -> local loopback -> login-request), storing the session + master token and renewing the session token automatically. It should be available from both opencode auth login and the TUI /connect dialog, with PAT auth unchanged.

I have an implementation ready and will open a PR linking this issue.