fix: infrastructure hardening and documentation improvements

- Add *.sqlite* patterns to .gitignore
- Expand .dockerignore to exclude chart/, docs/, .github/, etc.
- Add HEALTHCHECK instruction to Dockerfile
- Fix Helm chart: preserve JWT secret across upgrades (lookup),
  add securityContext, conditional PVC creation, resource defaults
- Remove hardcoded demo credentials from MCP.md
- Complete .env.example with all configurable environment variables

https://claude.ai/code/session_01SoQKcF5Rz9Y8Nzo4PzkxY8

chart/templates/pvc.yaml

@@ -1,3 +1,4 @@
+{{- if .Values.persistence.enabled }}
 apiVersion: v1
 kind: PersistentVolumeClaim
 metadata:
@@ -23,3 +24,4 @@ spec:
   resources:
     requests:
       storage: {{ .Values.persistence.uploads.size }}
+{{- end }}