fix: phase 0 quick wins — safety, naming, and portability

- Add helm.sh/resource-policy: keep to PVC (prevent data loss on uninstall)
- Add fail guard for empty name value in Helm templates
- Fix Makefile IMAGE_NAME from antigravity to devcontainer
- Pin busybox:1.37, homeassistant:v6.7.1, playwright:v0.0.68 (was latest/stable)
- Set imagePullPolicy: IfNotPresent on pinned sidecars
- Remove fetch/sequentialthinking from .mcp.json (sidecars removed from chart)
- Default storage.className to empty (use cluster default, was ceph-filesystem)
- Default Happy Coder URLs to empty (was private farh.net endpoints)
- Broaden githubRepo schema to accept GitLab/Gitea URLs
- Add unknown IDE warning before VSCode fallback
- Add mkdir -p before credential file write (fix fresh PVC boot)
- Guard app user existence in cont-init-user.sh
- Add NOTES.txt post-install template with port-forward and secret hints
- Add standard app.kubernetes.io/* labels and separate selectorLabels

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

chart/templates/_helpers.tpl

@@ -2,6 +2,9 @@
 Resource name prefix: devcontainer-{name}
 */}}
 {{- define "devcontainer.fullname" -}}
+{{- if not .Values.name }}
+{{- fail "values.name is required and must not be empty" }}
+{{- end }}
 {{- printf "devcontainer-%s" .Values.name }}
 {{- end }}
 
@@ -25,6 +28,18 @@ Common labels
 {{- define "devcontainer.labels" -}}
 app: devcontainer
 instance: {{ .Values.name }}
+app.kubernetes.io/name: devcontainer
+app.kubernetes.io/instance: {{ .Values.name }}
+app.kubernetes.io/managed-by: {{ .Release.Service }}
+helm.sh/chart: {{ .Chart.Name }}-{{ .Chart.Version | replace "+" "_" }}
+{{- end }}
+
+{{/*
+Selector labels — keep narrow since changing these requires recreating the Deployment
+*/}}
+{{- define "devcontainer.selectorLabels" -}}
+app: devcontainer
+instance: {{ .Values.name }}
 {{- end }}
 
 {{/*