feat: add Helm CLI and built-in web file manager

- Install Helm v3.17.1 in Dockerfile for chart development (closes #49)
- Add fileManager toggle using base image's WEB_FILE_MANAGER (closes #11)
- Wire WEB_FILE_MANAGER env vars in deployment template
- Update CLAUDE.md, README.md with new features and values

Generated with [Claude Code](https://claude.ai/code)
via [Happy](https://happy.engineering)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

chart/templates/deployment.yaml

@@ -69,6 +69,16 @@ spec:
               value: {{ .Values.display.height | quote }}
             - name: SECURE_CONNECTION
               value: {{ .Values.display.secureConnection | quote }}
+            {{- if .Values.fileManager.enabled }}
+            - name: WEB_FILE_MANAGER
+              value: "1"
+            - name: WEB_FILE_MANAGER_ALLOWED_PATHS
+              value: {{ .Values.fileManager.allowedPaths | quote }}
+            {{- if .Values.fileManager.deniedPaths }}
+            - name: WEB_FILE_MANAGER_DENIED_PATHS
+              value: {{ .Values.fileManager.deniedPaths | quote }}
+            {{- end }}
+            {{- end }}
             - name: HAPPY_HOME_DIR
               value: {{ .Values.happy.homeDir | quote }}
             - name: HAPPY_EXPERIMENTAL