feat(cyberchef): Gateway-API as an alternative to the Ingress (pilot)

The Gateway-API pilot of Gitea #114: one chart, the convention, the CI that
holds it. The remaining 20 charts follow in their own PRs.

The form, additive and off by default:

    httpRoute:
      enabled: false     # counterpart to ingress.enabled
      parentRefs: []     # the Gateway - a platform object
      hostnames: []      # empty = [ingress.domain]

Only HTTPRoute with parentRefs is rendered: no Gateway, no gatewayClassName,
no Certificate, and no implementation-specific policy object. That subset is
identical on nginx-gateway-fabric, Cilium, Envoy Gateway and Istio, which is
what lets the implementation be chosen later without touching the charts
again. Class and certificate move to the platform.

Four guards, all against silent failures:

  - mutually exclusive with ingress.enabled, with a render abort naming BOTH
    value paths. A migration runs over a second hostname, not in parallel.
  - parentRefs mandatory in Gateway mode, render abort on the empty list: a
    route without a parent is created, is schema-valid, and routes nothing.
  - hostnames empty means [ingress.domain], so the hostname has one source.
  - the mode is a VALUE, not auto-detection: .Capabilities.APIVersions is
    unreliable at template time and a missing CRD fails at install time.

ingress.clusterIssuer was already only read inside the Ingress template, so
the "conditionally required" half of #114 needed no change in this chart -
checked rather than assumed, and it has to be re-checked per chart in the
sweep.

CI, both halves, because neither covers the other:

  - the install-test installs cyberchef in GATEWAY mode against the REAL
    Gateway-API CRDs (standard channel v1.6.3, pinned and Renovate-tracked,
    applied --server-side). A schema-less stub would accept a malformed route
    and prove only that something was created. The Ingress path of this one
    chart is no longer installed; it is a built-in type that never routed in
    k3d anyway, and helm lint renders this chart's defaults - Ingress mode -
    on every PR.
  - ci/run-httproute-match-test.sh, over every chart on every PR: every
    backendRefs entry must name a Service, on a port, that the SAME render
    creates, and parentRefs must not be empty. The CRDs accept both of those
    mistakes, so the schema cannot catch them, and the only report would be a
    route status no controller writes in CI.

What stays unprovable, and is written down instead of implied: that traffic
flows. No Gateway controller runs in k3d.

Minor: additive with unchanged defaults, proven by an empty helm template
diff against origin/main for the default values.

Part of #114

cyberchef/values.yaml

@@ -68,13 +68,60 @@ cyberchef:
       ephemeralStorage: 10Mi
 
 ingress:
-  # Set to false to omit the Ingress entirely (the required domain and
-  # clusterIssuer values are then not needed either, because they are only
-  # read inside the Ingress template).
+  # Set to false to omit the Ingress entirely (the required clusterIssuer value
+  # is then not needed either, because it is only read inside the Ingress
+  # template). Mutually exclusive with httpRoute.enabled below: with both true
+  # the render aborts, naming both values.
   enabled: true
   clusterIssuer: null
+  # The public hostname of this release. Read by the Ingress AND - when
+  # httpRoute.hostnames is empty - by the HTTPRoute, so it stays the single
+  # source of truth for the hostname in both modes.
   domain: null
   className: nginx
   # Extra annotations for the Ingress; merged with the cert-manager
   # cluster-issuer annotation the chart always sets.
+  #
+  # THESE HAVE NO COUNTERPART IN GATEWAY MODE. The Gateway API has no
+  # annotation channel for controller behaviour, so everything configured here
+  # - external auth in front of an app that has no login of its own, for
+  # instance - is simply gone when httpRoute.enabled is used instead. It is
+  # then the Gateway's business, or that of an implementation-specific policy
+  # object this chart deliberately does not render.
   annotations: {}
+
+# Gateway-API alternative to the Ingress above (Gitea #114). Off by default, so
+# an existing release is unaffected; exactly one of ingress.enabled and
+# httpRoute.enabled may be true.
+#
+# The chart renders ONLY an HTTPRoute with parentRefs - no Gateway, no
+# gatewayClassName, no Certificate and no implementation-specific policy
+# object. Class and certificate belong to the Gateway and therefore to the
+# platform, which is what keeps this chart independent of whether the cluster
+# runs nginx-gateway-fabric, Cilium, Envoy Gateway or Istio.
+#
+# The Gateway-API CRDs must be installed in the cluster: the chart does not and
+# cannot detect them (.Capabilities.APIVersions is unreliable at template
+# time), so with httpRoute.enabled: true and no CRDs the INSTALL fails.
+httpRoute:
+  enabled: false
+  # The Gateway(s) this route attaches to - a platform object, usually in
+  # another namespace, which must allow this namespace in its listener's
+  # allowedRoutes. One entry per parent, the fields are the Gateway API's
+  # ParentReference (name, and optionally namespace, sectionName, port, group,
+  # kind), passed through unchanged:
+  #
+  #   parentRefs:
+  #     - name: public
+  #       namespace: gateway
+  #       sectionName: https
+  #
+  # REQUIRED while httpRoute.enabled is true - the render aborts on an empty
+  # list, because a route without a parent is created, is valid and routes
+  # nothing, with no event to say so.
+  parentRefs: []
+  # Empty means [ingress.domain], so the hostname has one source of truth. Set
+  # explicitly only to publish under a different or an additional name - which
+  # is how a migration from the Ingress runs: the HTTPRoute takes a second
+  # hostname while the Ingress keeps ingress.domain.
+  hostnames: []