**Root Cause:**
- Auth system was looking for 'keycloak-session' cookies
- But actual OIDC system uses 'nuxt-oidc-auth' cookies
- This caused authentication failures for file previews and other endpoints
**Files Updated:**
- server/utils/auth.ts: Updated to check 'nuxt-oidc-auth' cookie
- server/api/auth/session.ts: Updated cookie name references
- server/api/auth/logout.ts: Updated cookie deletion
- server/api/auth/keycloak/callback.ts: Updated cookie creation
**Result:**
- File previews should now work for authenticated users
- All authentication endpoints now use consistent cookie names
- Both x-tag headers and OIDC sessions work correctly