fix: use AUTHENTIK_USERNAME/PASSWORD env vars to match production

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/auth/service.py

@@ -296,7 +296,7 @@ class AuthService:
         if data.get("component") == "ak-stage-identification":
             resp = await client.post(
                 flow_url,
-                json={"uid_field": settings.authentik_admin_user},
+                json={"uid_field": settings.authentik_username},
                 headers=headers,
             )
             resp.raise_for_status()
@@ -312,7 +312,7 @@ class AuthService:
         if data.get("component") == "ak-stage-password":
             resp = await client.post(
                 flow_url,
-                json={"password": settings.authentik_admin_password},
+                json={"password": settings.authentik_password},
                 headers=headers,
             )
             resp.raise_for_status()
@@ -342,8 +342,8 @@ class AuthService:
         Returns:
             BulkSyncResultSchema with counts of created/updated/failed users
         """
-        if not settings.authentik_admin_user or not settings.authentik_admin_password:
-            raise ValueError("AUTHENTIK_ADMIN_USER and AUTHENTIK_ADMIN_PASSWORD must be configured")
+        if not settings.authentik_username or not settings.authentik_password:
+            raise ValueError("AUTHENTIK_USERNAME and AUTHENTIK_PASSWORD must be configured")
 
         created = 0
         updated = 0