fix DB password rotation desync in 5 stacks

Vault DB engine rotates passwords weekly but 5 stacks baked passwords
at Terraform plan time, causing stale credentials until next apply.

- real-estate-crawler: add vault-database ESO, use secret_key_ref in 3 deployments
- nextcloud: switch Helm chart to existingSecret for DB password
- grafana: add vault-database ESO, use envFromSecrets in Helm values
- woodpecker: use extraSecretNamesForEnvFrom, remove plan-time data source chain
- affine: add vault-database ESO, use secret_key_ref in deployment + init container

stacks/platform/modules/monitoring/main.tf

@@ -23,10 +23,6 @@ variable "pve_password" {
   type      = string
   sensitive = true
 }
-variable "grafana_db_password" {
-  type      = string
-  sensitive = true
-}
 variable "grafana_admin_password" {
   type      = string
   sensitive = true