feat!: NetworkPolicy in six more charts, on by default

bentopdf, apache-tika, gotenberg, rss-bridge, searxng, ytdlp-web-player. One
major each, networkPolicy.enabled defaults to true.

Three of them differ from the simple case in ways worth naming:

GOTENBERG gets DNS-only egress as a deliberate, documented trade. It drives a
headless Chromium, and 3000 is its probe port - so it is reachable from the
whole cluster by default, and an egress rule for 80/443 would turn a service
anyone can POST to into a way of fetching arbitrary URLs. The price is the
remote-asset half of HTML conversion: inline content converts, images the page
would have fetched silently do not. That degrades a PDF instead of failing a
pod, so nothing alerts on it, which is why it is in the template header, in
values.yaml and in NOTES.txt, with extraPorts: [80, 443] named as the knowing
opt-in.

RSS-BRIDGE, SEARXNG and YTDLP-WEB-PLAYER get the open internet on their web
ports, because reaching other people's servers IS the application and this
object cannot name a host. Said plainly in each, so none of them reads
stricter than it is. What the cap still buys is real: no other outbound port,
so a compromised pod reaches no database, no mail server and no SSH anywhere.

APACHE-TIKA and GOTENBERG render no Ingress - their consumers are other pods,
in other namespaces here - so neither gets an ingressController value and both
say in NOTES.txt that narrowing probeSources means listing the consumers'
namespaces in allowedNamespaces in the same change, or extraction and
conversion stop.

YTDLP-WEB-PLAYER names the gap this convention has: its oauth2-proxy subchart
renders its own Deployment with its own labels and ships no policy, so with the
proxy enabled the pod that actually faces the Ingress is unrestricted in both
directions. Nothing in this chart can change that - an upstream chart is
consumed as it comes - so it is written down instead.

ci/outline/test-values.yaml gains egress.extraPorts: [5556]. The CI dex runs
there rather than on 443, and Outline fetches the discovery document at boot -
so this is the chart's documented escape hatch used for exactly the case it was
written for, and the one place in the repo where the cap's upgrade risk is
actually exercised.

Part of #5

bentopdf/templates/NOTES.txt

@@ -153,3 +153,49 @@ bentopdf.env HAS NO EFFECT ON THE APP — AND THREE VALUES BREAK THE POD
   starts. Using them means also setting
   securityContext.container.readOnlyRootFilesystem: false.
 {{- end }}
+{{- if .Values.networkPolicy.enabled }}
+
+NETWORKPOLICY IS ACTIVE — WHAT IT CAPS, AND WHAT IT DOES NOT
+  {{ .Release.Name }}-{{ .Chart.Name }}-networkpolicy selects this workload's pods.
+  Inbound: TCP 8080 only. Outbound: DNS{{ with .Values.networkPolicy.egress }}{{ with .extraPorts }} plus TCP {{ join ", " . }}{{ end }}{{ end }} — the documents are
+  processed in the browser, so the pod needs nothing more.
+
+  Three limits belong in the same breath, because none of them is visible in
+  the object itself:
+
+  - EGRESS IS BY PORT, NEVER BY DESTINATION. A NetworkPolicy matches CIDRs and
+    selectors and cannot express a hostname, so every egress rule permits its
+    port to ANY address. That is a limit of the object, not a shortcut — this
+    cluster's CNI (Canal: Flannel plus Calico) has no FQDN rule either. An
+    outbound port the chart does not know about is BLOCKED: add it to
+    networkPolicy.egress.extraPorts, and expect to find out through an
+    application-level connection error rather than through this object.
+{{- if .Values.networkPolicy.probeSources }}
+  - THE PROBE PATH IS RESTRICTED in this release, because
+    networkPolicy.probeSources is set to
+      {{ join ", " .Values.networkPolicy.probeSources }}
+    Probes come from the IP of the WORKER NODE running the pod. If none of those
+    CIDRs covers the node this pod lands on, the kubelet's probes are dropped
+    and THE POD NEVER BECOMES READY — the rollout then times out and the symptom
+    looks like a broken application. Compare
+
+      kubectl -n {{ .Release.Namespace }} describe pod -l app={{ .Release.Name }}-{{ .Chart.Name }}-deployment
+
+    against `kubectl get node -o wide`.
+{{- else }}
+  - THE PROBED PORT IS OPEN INSIDE THE CLUSTER. networkPolicy.probeSources is
+    empty, so that rule carries no source selector at all and any pod the CNI
+    routes to can reach it. Not from the internet — but this is NOT pod-level
+    isolation. Narrowing it means listing the worker node IPs in
+    networkPolicy.probeSources, because the kubelet probes from the node's own
+    address and the chart cannot know it; a wrong guess there leaves the pod
+    permanently un-Ready.
+{{- end }}
+  - IT IS ONLY A BOUNDARY WHERE THE CNI ENFORCES POLICIES. Where it does not,
+    this object is accepted and filters nothing, so everything reads as
+    configured while nothing is filtered. `kubectl -n {{ .Release.Namespace }} get networkpolicy`
+    shows the object exists; only a connection attempt from an unrelated
+    namespace shows that it bites.
+
+  Switch it off with networkPolicy.enabled: false.
+{{- end }}