migrate all secrets from SOPS to Vault KV

- Add vault provider to root terragrunt.hcl (generated providers.tf)
- Delete stacks/vault/vault_provider.tf (now in generated providers.tf)
- Add 124 variable declarations + 43 vault_kv_secret_v2 resources to
  vault/main.tf to populate Vault KV at secret/<stack-name>
- Migrate 43 consuming stacks to read secrets from Vault KV via
  data "vault_kv_secret_v2" instead of SOPS var-file
- Add dependency "vault" to all migrated stacks' terragrunt.hcl
- Complex types (maps/lists) stored as JSON strings, decoded with
  jsondecode() in locals blocks

Bootstrap secrets (vault_root_token, vault_authentik_client_id,
vault_authentik_client_secret) remain in SOPS permanently.

Apply order: vault stack first (populates KV), then all others.

stacks/hackmd/main.tf

@@ -1,13 +1,13 @@
-variable "hackmd_db_password" {
-  type      = string
-  sensitive = true
-}
 variable "tls_secret_name" {
   type = string
 }
 variable "nfs_server" { type = string }
 variable "mysql_host" { type = string }
 
+data "vault_kv_secret_v2" "secrets" {
+  mount = "secret"
+  name  = "hackmd"
+}
 
 resource "kubernetes_namespace" "hackmd" {
   metadata {
@@ -103,7 +103,7 @@ resource "kubernetes_deployment" "hackmd" {
           env {
             name = "CMD_DB_URL"
             # value = format("%s%s%s", "postgres://codimd:", var.hackmd_db_password, "@localhost/codimd")
-            value = format("%s%s%s", "mysql://codimd:", var.hackmd_db_password, "@${var.mysql_host}/codimd")
+            value = format("%s%s%s", "mysql://codimd:", data.vault_kv_secret_v2.secrets.data["db_password"], "@${var.mysql_host}/codimd")
           }
           env {
             name  = "CMD_USECDN"

stacks/hackmd/providers.tf

@@ -1,7 +1,7 @@
 # Generated by Terragrunt. Sig: nIlQXj57tbuaRZEa
 variable "kube_config_path" {
-  type    = string
-  default = "~/.kube/config"
+  type      = string
+  default   = "~/.kube/config"
   sensitive = true
 }
 

stacks/hackmd/terragrunt.hcl

@@ -6,3 +6,8 @@ dependency "platform" {
   config_path  = "../platform"
   skip_outputs = true
 }
+
+dependency "vault" {
+  config_path  = "../vault"
+  skip_outputs = true
+}