vault: add ghp engine config-write + consumer policies (pre-step)

Step 2 of the ordered ghp plugin add. policies/ghp/admin.yaml grants the
terraform apply identities (tf_vault approle, woodpecker_terraform_vault k8s
role) create/update on ghp/config and ghp/roles/*; policies/ghp/creds/agent.yaml
grants the agents approle read on ghp/creds/agent.

Must merge + apply BEFORE the engine resources (terraform-vault#121): an approle
token's capabilities are fixed at login, so the deployer needs this policy active
in a prior apply before it can write ghp/config.

policies/ghp/admin.yaml

@@ -0,0 +1,37 @@
+# Allow the vault deployer to manage the ghp token secrets engine: its
+# connection config (seeded service token) and its token-minting roles.
+#
+# Scoped to ghp/* only, and deliberately excludes ghp/creds/* - minting tokens
+# is for consumers, not the deployer. ghp has NO rotate endpoint, so unlike the
+# gitea/netbox engines there is no config/rotate grant here. The plugin-catalog
+# grant needed to import the plugin is the shared, sudo-protected wildcard in
+# policies/sys/plugins/catalog/admin.yaml (already covers this plugin), and
+# mounting the engine uses the deployer's existing sys/mounts/* access, so no
+# new catalog/mount grant is added here (mirrors the gitea/netbox engines).
+---
+rules:
+  # Engine connection config (base_url, TLS, seeded service token).
+  - path: "ghp/config"
+    capabilities:
+      - create
+      - read
+      - update
+      - delete
+  # Token-minting roles.
+  - path: "ghp/roles/*"
+    capabilities:
+      - create
+      - read
+      - update
+      - delete
+      - list
+  - path: "ghp/roles"
+    capabilities:
+      - read
+      - list
+
+auth:
+  approle:
+    - tf_vault
+  k8s/au/syd1:
+    - woodpecker_terraform_vault

policies/ghp/creds/agent.yaml

@@ -0,0 +1,13 @@
+# Lets the agents AppRole mint ephemeral ghp agent tokens, so AI coding agents
+# authenticate to ghp as their own short-lived, least-privilege identity.
+# Reading ghp/creds/agent returns a lease-bound token scoped by the role
+# (token_type agent, contents:read). Mirrors the gitea/creds/unkin-agent binding.
+---
+rules:
+  - path: "ghp/creds/agent"
+    capabilities:
+      - read
+
+auth:
+  approle:
+    - agents