template-chart + README: values.schema.json, gate and null-safe helpers

Closes out the schema programme (#68) by moving what the 18 charts taught
into the reference implementation and the binding guidelines.

template-chart:
- values.schema.json as the reference schema: additionalProperties false
  on every chart-owned level, pod-spec passthrough left open, and the
  reasoning inline in the descriptions so a copy carries it along.
- defaultedDict and subBlock plus the per-block fallbacks for both
  security contexts, the three probes and resources, wired into both the
  Deployment and the StatefulSet.
- the reference itself violated guideline 1: its env block reads
  ingress.domain, so with the Ingress gated off it rendered an empty
  value. That read is now required(), and the comment says why - the
  template is what people copy, so it has to teach the guard, not the
  hole.

README, new section "Values that must not lie" with the five rules:
1. a value read outside its obvious template needs its own guard
   (matrix-synapse published '{"m.server": ":443"}' to federation without
   it, rendering cleanly and reporting healthy)
2. probes, contexts and resources through the null-safe helper, never
   behind an "if" - a guard removes the probe instead of showing a null
3. no liveness on an external dependency where a dependency-free path
   exists, otherwise document why on the helper
4. a fallback reproduces THIS chart's defaults, not the repo standard -
   calibre's readOnlyRootFilesystem: false is what keeps the runtime uid
   at 1000 instead of 911 and existing volume data readable
5. a probe default carries its context - port name, Host header, exec
   command - or the probe vanishes (teamspeak) or gets 403 (patchmon)

Plus the two mechanics that are easiest to lose: null reaches schema
validation only for keys WITHOUT a chart default (which is why the helper
and the ["object","null"] types each cover a case the other cannot), and
schemas must be validated against real bundle values - that step caught a
draft of mine that would have broken three live paperless releases.

CLAUDE.md: the new-chart checklist now names the schema and the
adaptation step, since the copied file is chart-specific and wrong until
it is adapted.

freesailarr is not covered: it is not on main yet (#59).

template-chart/values.yaml

@@ -63,8 +63,13 @@ xxx:
       protocol: TCP
       name: http
   env:
+    # Reference for guideline 1: ingress.domain is read HERE, outside the
+    # Ingress template, so it needs its own required(). Without it, switching
+    # the Ingress off via ingress.enabled would render an empty value and the
+    # workload would start with a broken address - silently. Copy this shape
+    # whenever a chart uses the domain for anything but the Ingress host.
     - name: NORMAL_ENV
-      value: "{{ .Values.ingress.domain }}"
+      value: '{{ required "A Domain/Host must be provided (ingress.domain)" .Values.ingress.domain }}'
     - name: ENV_FROM_SECRET
       valueFrom:
         secretKeyRef:
@@ -81,6 +86,10 @@ storage:
   storageClass: null
 
 ingress:
+  # Gates the whole Ingress template. Note that ingress.domain is ALSO read by
+  # the env block above, so it stays required even with the Ingress switched
+  # off; only clusterIssuer becomes unnecessary. Check this per chart instead
+  # of assuming either way (guideline 1).
   enabled: true
   clusterIssuer: null
   domain: null