GitLab

- Add admin menu permission check in CustomPageView (visibility + role)
- Sanitize SVG content with DOMPurify before v-html rendering (XSS prevention)
- Decouple router.go from dto package using anonymous struct
- Consolidate duplicate parseCustomMenuItems into dto.ParseCustomMenuItems
- Enhance menu item validation (count, length, ID uniqueness limits)
- Add audit logging for purchase_subscription and custom_menu_items changes
- Update API contract test to include custom_menu_items field
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Add configurable custom menu items that appear in sidebar, each rendering
an iframe-embedded external page. Includes shared URL builder with
src_host/src_url tracking, CSP frame-src multi-origin deduplication,
admin settings UI, and i18n support.

chore: bump version to 0.1.87.19
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

- 新增 /purchase 页面（iframe + 新窗口兜底）

- 管理员系统设置可配置开关与URL

- 非 simple mode 才在侧边栏展示入口