docs: update Connect flow for Data Connection Requests

[tnunamak]

Summary

• update the Quickstart, JavaScript SDK page, and integration guide for the Data Connection Request flow
• remove the legacy encryption-secret setup from the published path
• replace the stale provider list with the live source and scope APIs

Verification

• built a fresh Next.js app from the Quickstart against @opendatalabs/connect-js@1.19.0-staging.12
• npm run build passed for the generated app
• git diff --check

The docs use the normal latest install command and should merge after the SDK promotion.

Assisted-by: AI

[tnunamak]

Closing this draft documentation update. It changed a non-canonical SDK reference while the published /docs/javascript-sdk page is sourced from custom_pages/javascript-sdk.md; the docs need a complete route-to-source audit and a snippet test against the released SDK before reopening a focused replacement.