refactor: one self-contained folder per platform service

Each platform/apps/<service>/ now holds its own application.yaml
(multi-source: chart + values + raw-manifest extras), values.yaml, and
any extra manifests (HTTPRoute, RBAC, ClusterSecretStore) together,
replacing the split apps/*.yaml + manifests/*/ + separate *-config
Application pattern.

Root platform-app.yaml now recurses platform/apps/*/application.yaml
only. Extras get a resource-level sync-wave (1) so they still land
after their service's Helm chart within the same Application sync.

Also adds an HTTPRoute for vault (vault.fireflylab.local) - exposed
same as every other service here, accepted as LAN-only exposure.

platform/apps/external-secrets/clustersecretstore.yaml

@@ -0,0 +1,19 @@
+apiVersion: external-secrets.io/v1beta1
+kind: ClusterSecretStore
+metadata:
+  name: vault-backend
+  annotations:
+    argocd.argoproj.io/sync-wave: "1"
+spec:
+  provider:
+    vault:
+      server: "http://vault.vault.svc.cluster.local:8200"
+      path: kv
+      version: v2
+      auth:
+        kubernetes:
+          mountPath: kubernetes
+          role: external-secrets
+          serviceAccountRef:
+            name: external-secrets-vault-auth
+            namespace: external-secrets