template-chart: seccomp profile, unprivileged port, and two placeholder fixes

Five changes to the scaffold every future chart is copied from:

1. seccompProfile.type: RuntimeDefault in the pod security context, in
   line with the rest of the seccomp series (#84). Pod context, because
   from there it also covers init containers and any container added
   later without being repeated.

2. containerPort 80 -> 8080, clearing AVD-KSV-0117. Note that the usual
   justification for this does not hold: a non-root container CAN bind
   port 80 on current Kubernetes, because the kubelet sets
   net.ipv4.ip_unprivileged_port_start=0 in the pod network namespace.
   Measured, not assumed - see the values.yaml comment. The reason to
   stay above 1024 is that this is a runtime default rather than a
   guarantee, and that every real chart here already does.

3. The ConfigMap placeholder key is renamed from the literal "key" to
   "example-setting", clearing AVD-KSV-01010 (secret-scanner patterns
   match any key named "key").

4. The image placeholder is fully qualified as ghcr.io/ORG/IMAGE, so the
   template stops teaching the unqualified form that produced the
   repo's unqualified Docker Hub images.

5. env values are rendered through "quote". Without it a value like
   "8080" renders as a YAML number and the API server rejects the whole
   manifest ("cannot unmarshal number into Go struct field
   EnvVar.value of type string"). Every real chart in the repo already
   quotes here; only the template did not. Found by instantiating the
   template and installing it, not by rendering it.

Verified by instantiating the scaffold into a working chart per the
README procedure and installing it in k3d: the workload becomes Ready,
the Service routes to the app on 8080 and an ephemeral container added
to the running pod inherits Seccomp: 2 from the pod context.

Refs #84

template-chart/templates/_helpers.tpl

@@ -229,7 +229,8 @@ guidelines"):
       "runAsUser" 20000
       "runAsGroup" 1000
       "fsGroup" 1000
-      "fsGroupChangePolicy" "Always" -}}
+      "fsGroupChangePolicy" "Always"
+      "seccompProfile" (dict "type" "RuntimeDefault") -}}
 {{- include "xxx.defaultedDict" (dict "defaults" $defaults "given" $given "path" "xxx.securityContext.pod") -}}
 {{- end -}}