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/block-weekends/policy_test.rego

@@ -0,0 +1,12 @@
+package rules.block_weekends_test
+
+import data.rules.block_weekends as rule
+import rego.v1
+
+test_scenarios[scenario_name] if {
+	some scenario_name, scenario in data.scenarios
+	actual := {code | code := rule.violations[_].code} with input as scenario.input with data.deploygate as scenario.data
+	expected := {code | code := scenario.expect.violations[_]}
+	actual == expected
+	rule.allow == scenario.expect.allow with input as scenario.input with data.deploygate as scenario.data
+}