feat: add DB social auth config model

[smshagor-dev]

No description provided.

[vercel]

Deployment failed for project syncchat with the following error:

Resource is limited - try again in 24 hours (more than 100, code: "api-deployments-free-per-day").

Learn More: https://vercel.com/smshagor-devs-projects?upgradeToPro=build-rate-limit

[vercel]

Deployment failed for project syncchat-api with the following error:

Resource is limited - try again in 24 hours (more than 100, code: "api-deployments-free-per-day").

Learn More: https://vercel.com/smshagor-devs-projects?upgradeToPro=build-rate-limit

[vercel]

Deployment failed for project syncchat with the following error:

Resource is limited - try again in 1 day (more than 100, code: "api-deployments-free-per-day").

Learn More: https://vercel.com/smshagor-devs-projects?upgradeToPro=build-rate-limit

[smshagor-dev]

Conflict resolution status: the DB-backed social auth work from this PR was completed and merged via PR #10. The remaining deployment-routing cleanup from fix/admin-db-config-sidebar is now isolated in PR #11, rebased on current main, conflict-free, and marked ready for review. GitHub Actions passes; the only reported deployment failure is Vercel's daily free-plan deployment limit.