[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/infra/backend.tf

@@ -0,0 +1,6 @@
+# Generated by Terragrunt. Sig: nIlQXj57tbuaRZEa
+terraform {
+  backend "local" {
+    path = "/Users/viktorbarzin/code/infra/state/stacks/infra/terraform.tfstate"
+  }
+}

stacks/infra/providers.tf

@@ -0,0 +1,25 @@
+# Generated by Terragrunt. Sig: nIlQXj57tbuaRZEa
+terraform {
+  required_providers {
+    proxmox = {
+      source  = "telmate/proxmox"
+      version = "3.0.2-rc07"
+    }
+  }
+}
+
+variable "kube_config_path" {
+  type    = string
+  default = "~/.kube/config"
+}
+
+variable "proxmox_pm_api_url" { type = string }
+variable "proxmox_pm_api_token_id" { type = string }
+variable "proxmox_pm_api_token_secret" { type = string }
+
+provider "proxmox" {
+  pm_api_url          = var.proxmox_pm_api_url
+  pm_api_token_id     = var.proxmox_pm_api_token_id
+  pm_api_token_secret = var.proxmox_pm_api_token_secret
+  pm_tls_insecure     = true
+}