[ci skip] Move Terraform modules into stack directories

Move all 88 service modules (66 individual + 22 platform) from
modules/kubernetes/<service>/ into their corresponding stack directories:

- Service stacks: stacks/<service>/module/
- Platform stack: stacks/platform/modules/<service>/

This collocates module source code with its Terragrunt definition.
Only shared utility modules remain in modules/kubernetes/:
ingress_factory, setup_tls_secret, dockerhub_secret, oauth-proxy.

All cross-references to shared modules updated to use correct
relative paths. Verified with terragrunt run --all -- plan:
0 adds, 0 destroys across all 68 stacks.

stacks/platform/modules/monitoring/prometheus.tf

@@ -0,0 +1,58 @@
+
+resource "kubernetes_persistent_volume_claim" "prometheus_server_pvc" {
+  metadata {
+    name      = "prometheus-iscsi-pvc"
+    namespace = kubernetes_namespace.monitoring.metadata[0].name
+  }
+
+  spec {
+    access_modes = ["ReadWriteOnce"]
+    resources {
+      requests = {
+        storage = "15Gi"
+      }
+    }
+    # storage_class_name = "standard"
+    volume_name = "prometheus-iscsi-pv"
+  }
+}
+
+resource "kubernetes_persistent_volume" "prometheus_server_pvc" {
+  metadata {
+    name = "prometheus-iscsi-pv"
+  }
+  spec {
+    capacity = {
+      storage = "15Gi"
+    }
+    access_modes = ["ReadWriteOnce"]
+    persistent_volume_source {
+      nfs {
+        path   = "/mnt/main/prometheus"
+        server = "10.0.10.15"
+      }
+      # iscsi {
+      #   fs_type       = "ext4"
+      #   iqn           = "iqn.2020-12.lan.viktorbarzin:storage:monitoring:prometheus"
+      #   lun           = 0
+      #   target_portal = "iscsi.viktorbarzin.me:3260"
+      # }
+
+    }
+    persistent_volume_reclaim_policy = "Retain"
+    volume_mode                      = "Filesystem"
+  }
+}
+
+resource "helm_release" "prometheus" {
+  namespace        = kubernetes_namespace.monitoring.metadata[0].name
+  create_namespace = true
+  name             = "prometheus"
+
+  repository = "https://prometheus-community.github.io/helm-charts"
+  chart      = "prometheus"
+  # version    = "15.0.2"
+  version = "25.8.2"
+
+  values = [templatefile("${path.module}/prometheus_chart_values.tpl", { alertmanager_mail_pass = var.alertmanager_account_password, alertmanager_slack_api_url = var.alertmanager_slack_api_url, tuya_api_key = var.tiny_tuya_service_secret, haos_api_token = var.haos_api_token })]
+}