Add vault-plugin-secrets-arrstack repo

vault-plugin-secrets-arrstack is a new Vault/OpenBao secrets engine that
dynamically mints arrproxy machine (per-user) API tokens, enabling
terraform-driven onboarding of *arr services. It needs a Gitea repo to
host its source before CI and releases can be wired up.

- add config/git.unkin.net/unkin/repository/vault-plugin-secrets-arrstack.yaml
- public repo, default branch main, delete-branch-after-merge, squash-only
- Owners-only merge with required pre-commit/build/test Woodpecker checks

config/git.unkin.net/unkin/repository/vault-plugin-secrets-arrstack.yaml

@@ -0,0 +1,21 @@
+description: "Vault/OpenBao secrets engine minting dynamic arrproxy per-user API tokens"
+private: false
+default_branch: "main"
+default_delete_branch_after_merge: true
+# Squash-only: the gitea provider has no "default merge style", so we restrict
+# the allowed styles to squash to force it.
+allow_merge_commits: false
+allow_rebase: false
+allow_rebase_explicit: false
+allow_squash_merge: true
+branch_protection:
+  - rule_name: "main"
+    merge_whitelist_teams:
+      - "Owners"
+    enable_push: false
+    status_check_contexts:
+      - "ci/woodpecker/pr/pre-commit"
+      - "ci/woodpecker/pr/build"
+      - "ci/woodpecker/pr/test"
+    approval_whitelist_teams:
+      - "Owners"