modules: add env/envs parameter to app_roles + app_policy (multi-env)

Phase A of the multi-environment evolution agreed in the erp repo design
thread. Both modules gain an optional env coordinate that defaults to
"prod"; by the elision rule, env=prod produces the existing single-env
derived names character-for-character, so every existing app's tofu plan
should be a no-op.

app_roles (per-instance module — caller iterates over envs):
- variables.tf: add optional env = "prod"
- main.tf: compute local.instance via elision rule + local.owner_role
  (snake-case <name>_<env>_role for the Postgres owner)
- main.tf: substitute local.name -> local.instance in all derived names
  (dynamic role name, k8s role name, SA bindings, token_policies)
- outputs.tf: add env + instance outputs; kvv2_path_prefix now derives
  from local.instance (== local.name when env=prod -> backwards-compat)

app_policy (per-repo module — accepts list of envs):
- variables.tf: add optional envs = ["prod"]
- main.tf: compute local.instances + local.non_prod_instances
- main.tf: refactor kvv2 ops rules to dynamic blocks iterating local.instances
  preserving the original rule order (data, delete, undelete, destroy,
  metadata) so prod-only apps render a byte-identical policy document
- main.tf: allowed_parameter blocks for k8s role's bound_service_account_*
  and token_policies use comprehensions over local.instances
- main.tf: keep vault_policy.app (the env=prod runtime policy) at its
  original address; add vault_policy.app_non_prod via for_each over
  non_prod_instances for the other envs

Top-level wiring:
- iac/variables.tf: add envs = optional(list(string), ["prod"]) to the
  applications set(object) type
- iac/main.tf: pass envs = each.value.envs through to app_policies

`tofu validate` passes. Every existing app's tofu plan should report no
changes because: (1) env="prod" defaults are used everywhere, (2) the
elision rule makes local.instance == local.name for prod, (3) dynamic
rule blocks preserve declaration order, (4) the new app_non_prod resource
is created via for_each over an empty set when no non-prod envs are
declared.

Phase B (factory postgres iac + argocd + runbook docs) and Phase D
(erp iac/main.tf for_each + activate sandbox) follow in their own PRs.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

hashicorp-vault/iac/variables.tf

@@ -15,5 +15,9 @@ variable "applications" {
     policies = optional(list(string), [])
     service_account_names = optional(list(string), [])
     service_account_namespaces = optional(list(string), [])
+    # Multi-env extension: list of envs this app deploys to. Defaults to ["prod"] for
+    # every existing app — backwards compatible by the elision rule. Non-prod envs
+    # produce additional runtime policies named "<name>-<env>".
+    envs = optional(list(string), ["prod"])
   }))
 }