fix(auth): support OIDC federated logout

[cxymds]

Pull Request

Description

Add OIDC federated logout support to the console so OIDC users exit through the backend logout endpoint instead of only clearing local STS state.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Code refactoring
• Performance improvement
• Test improvements
• Security fix

Testing

• Unit tests added/updated
• Manual testing completed

pnpm tsc --noEmit
pnpm lint contexts/auth-context.tsx components/user/dropdown.tsx lib/oidc.ts 'app/(auth)/auth/oidc-callback/page.tsx'
pnpm prettier --check contexts/auth-context.tsx components/user/dropdown.tsx lib/oidc.ts 'app/(auth)/auth/oidc-callback/page.tsx'

Checklist

• Code follows the project's style guidelines
• Self-review completed
• TypeScript types are properly defined
• All commit messages are in English (Conventional Commits)
• All existing tests pass
• No new dependencies added, or they are justified

Related Issues

Closes #103

Screenshots (if applicable)

N/A

Additional Notes

This PR expects the paired RustFS backend change to provide /rustfs/admin/v3/oidc/logout and the callback logoutToken.