fix(ERP-245): separate broken-file marker from image src URL

fix(ERP-245): separate broken-file marker from image src URL

- WriteOffsErp::getImagesList() previously set $imageThumbRow='broken_file-error'
  as sentinel, then built src="/broken_file-error" causing Yii2 to try routing
  it as a controller action → repeated 404 errors in production logs
- Separated marker (kept in $relaFileName for alt/debug) from URL (now points
  to valid static placeholder /images/no-image.svg)
- Added erp24/web/images/no-image.svg: lightweight SVG fallback served by nginx

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