feat: scaffold deployment-policies monorepo

OPA/Rego deployment gateway policies: 5 rules (valid-environment,
require-approvals, no-self-approval, block-weekends, freeze-window),
a deploy-gate combining them, JSON schemas, scenario-driven tests,
Gitea Actions CI (verify + publish to generic registry), changesets
versioning, Makefile and scripts.

policies/rules/no-self-approval/policy.rego

@@ -0,0 +1,25 @@
+# METADATA
+# schemas:
+#   - input: schema["input"]
+#   - data: schema["data"]
+
+package rules.no_self_approval
+
+import rego.v1
+
+default allow := false
+
+allow if {
+	count(violations) == 0
+}
+
+violations contains {"code": "self_approval", "message": sprintf("approval by %q is the deployment requestor", [input.deployment.requested_by])} if {
+	some approval in input.approvals
+	approval.active
+	approval.by == input.deployment.requested_by
+}
+
+violations contains {"code": "missing_requestor", "message": "deployment has no requestor"} if {
+	input.deployment
+	not input.deployment.requested_by
+}