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

umami/manifests/secret.yaml

@@ -14,9 +14,9 @@ spec:
   data:
     - secretKey: database-url
       remoteRef:
-        key: applications/umami
+        key: umami
         property: DATABASE_URL
     - secretKey: hash-salt
       remoteRef:
-        key: applications/umami
+        key: umami
         property: HASH_SALT