add: actual-budget-exporter app

Prometheus exporter for Actual Budget. actual_server itself stays in
homelab-docker-compose-prod (host docker-compose), exporter only scrapes it
over LAN and exposes /metrics via a ServiceMonitor. No HTTPRoute. Password
and budget ID come from a hand-created Secret, not committed.

apps/actual-budget-exporter/application.yaml

@@ -0,0 +1,17 @@
+apiVersion: argoproj.io/v1alpha1
+kind: Application
+metadata:
+  name: actual-budget-exporter
+  namespace: argocd
+spec:
+  project: default
+  source:
+    repoURL: https://gitea.fireflylab.cc/duynguyen/homelab-services.git
+    targetRevision: main
+    path: apps/actual-budget-exporter/chart
+  destination:
+    server: https://kubernetes.default.svc
+    namespace: actualbudget
+  syncPolicy:
+    syncOptions:
+      - CreateNamespace=true