feat(opa): add conftest OPA policies and pre-commit hook

Adds three policy files under policy/ plus a pre-commit hook that
runs conftest against all staged YAML manifests (excluding chart
templates).

Policies:
  no_ingress.rego
    Deny Ingress resources — cluster uses Gateway API only.

  gateway_api.rego
    HTTPRoute/TLSRoute: require explicit group/kind on parentRefs and
    group/kind/weight on backendRefs (PR #162, #165).
    Gateway: require explicit group on certificateRefs (PR #153).
    All fields are defaulted by the controller; omitting them causes
    permanent ArgoCD OutOfSync.

  resource_normalization.rego
    CPU integer: deny unquoted integer cpu values (PR #163).
    CPU milliCPU: deny values like 1000m/2000m that normalise to "1"/"2" (PR #164).
    Memory Mi→Gi: deny 1024Mi/2048Mi etc. that normalise to 1Gi/2Gi (PR #163).
    clusterIP null: deny Service with explicit null clusterIP (PR #166).

Also fixes all existing violations found by the new policies across
puppet deployments and reposync cronjobs (resource normalization).
kanidm/tlsroute.yaml and puppet/service_puppetdb.yaml are excluded
from this commit as they are addressed in PRs #165 and #166.

.pre-commit-config.yaml

@@ -40,3 +40,10 @@ repos:
         entry: ci/validate-no-secrets.sh
         language: system
         pass_filenames: false
+      - id: conftest_policies
+        name: OPA policy checks (conftest)
+        entry: conftest test --policy policy/
+        language: system
+        types: [yaml]
+        exclude: ".*/charts/.*|.*/templates/.*|\\.woodpecker/.*"
+        pass_filenames: true