feat(auth): Add Discord OAuth Provider (#5552)

.cursor/rules/security-patterns.mdc

@@ -22,6 +22,7 @@ Coolify implements **defense-in-depth security** with multiple layers of protect
   - Google OAuth
   - Microsoft Azure AD
   - Authentik
+  - Discord
   - GitHub (via GitHub Apps)
   - GitLab
 

.cursor/rules/technology-stack.mdc

@@ -90,7 +90,7 @@ alwaysApply: false
 - **Purpose**: OAuth provider integration
 - **Providers**:
   - GitHub, GitLab, Google
-  - Microsoft Azure, Authentik
+  - Microsoft Azure, Authentik, Discord
   - Custom OAuth implementations
 
 ## Background Processing