Add support for custom OAuth providers

Bounty Amount

$2,000,000,000USDC

Claimed by

maria-dev

enhancementhelp wanted

Issue Description

Allow users to configure their own OAuth providers beyond GitHub, Google, and Microsoft.

**Requirements:**

Support generic OAuth 2.0 / OIDC providers

Admin UI for configuring providers

Token refresh handling

Proper error messages for misconfigured providers

Awaiting review

Work Submitted

Awaiting review