fix(ttsreader): pin VoicePreview CacheDirectory to /data PVC

Day 8 disk-cache warmer crashes on production with
'Read-only file system : /home/app/data' because the relative default
'data/voice-previews' resolves under runAsNonRoot HOME (read-only with
readOnlyRootFilesystem=true). Pin to /data/voice-previews so the cache
lands on the writable PVC mount alongside ttsreader.db, audio output,
and jobs root.

Image v202604272216 (already on nodes) is unaffected by this — only
the env routing changes. ArgoCD reconciles + rollout restart picks up
the new env without rebuild.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/fc-ttsreader/fc-ttsreader.yaml

@@ -573,6 +573,12 @@ spec:
               value: "/data/logs"
             - name: TtsReader__Runtime__SmokeStatePath
               value: "/data/ops/smoke-status.json"
+            # Sprint E Day 8 voice-preview disk cache — writes WAVs under
+            # this directory. Default "data/voice-previews" resolves to
+            # the read-only $HOME path under runAsNonRoot=true. Pin to
+            # the writable PVC mount.
+            - name: TtsReader__Preview__CacheDirectory
+              value: "/data/voice-previews"
             - name: Auth__ApiKey
               valueFrom:
                 secretKeyRef: