REFACTOR(repo): move vault/ to manifests/

- Move ExternalSecret files from vault/ to manifests/secret.yaml
- Merge multiple secrets with --- separator (immich)
- Update kustomization.yaml references
- Remove vault/ folders

Apps: umami, immich, code-server

umami/manifests/secret.yaml

@@ -0,0 +1,22 @@
+apiVersion: external-secrets.io/v1
+kind: ExternalSecret
+metadata:
+  name: umami-password
+  namespace: umami
+spec:
+  refreshInterval: 1h
+  secretStoreRef:
+    kind: ClusterSecretStore
+    name: vault-backend
+  target:
+    name: umami-password
+    creationPolicy: Owner
+  data:
+    - secretKey: database-url
+      remoteRef:
+        key: applications/umami
+        property: DATABASE_URL
+    - secretKey: hash-salt
+      remoteRef:
+        key: applications/umami
+        property: HASH_SALT