REFACTOR(secrets): flatten Vault paths

- Change secret paths from <category>/<app> to <app>
- applications/code-server → code-server
- applications/umami → umami
- databases/postgresql → postgresql
- cluster-infrastructure/authelia → authelia

code-server/manifests/secret.yaml

@@ -14,5 +14,5 @@ spec:
   data:
     - secretKey: password
       remoteRef:
-        key: applications/code-server
+        key: code-server
         property: PASSWORD