chore(authentik): bump 2026.5.2 -> 2026.5.3 (bugfix/security patch)

Pure bugfix/security patch per upstream release notes — no breaking
changes or migration steps. Bumps both authentik-server and
authentik-worker (embedded outpost updates with the server).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

stacks/authentik/docker-compose.yml

@@ -8,7 +8,7 @@
 services:
   authentik-server:
     container_name: authentik_server
-    image: ghcr.io/goauthentik/server:2026.5.2
+    image: ghcr.io/goauthentik/server:2026.5.3
     restart: unless-stopped
     command: server
     networks: [authentik, edge]
@@ -36,7 +36,7 @@ services:
 
   authentik-worker:
     container_name: authentik_worker
-    image: ghcr.io/goauthentik/server:2026.5.2
+    image: ghcr.io/goauthentik/server:2026.5.3
     restart: unless-stopped
     command: worker
     networks: [authentik]