Add external link ordering controls

[paullizer]

Summary

• add accessible Move Up and Move Down controls for saved external links
• keep visible row order and the existing external_links_json save payload synchronized
• rerender boundary states after add, edit, delete, and move operations
• replace the touched dynamic row markup with safe DOM construction and HTTP/HTTPS URL normalization
• add functional and Azure Playwright regression coverage, fix documentation, release notes, and version 0.250.102

Validation

• python -m pytest functional_tests\test_external_link_ordering.py ui_tests\test_admin_external_link_ordering.py -q (2 passed, 1 skipped because authenticated UI environment variables are not configured locally)
• node --check application\single_app\static\js\admin\admin_settings.js
• python scripts\check_xss_sinks.py application\single_app\static\js\admin\admin_settings.js --base-sha HEAD^ --head-sha HEAD
• git -c core.whitespace=blank-at-eol,blank-at-eof,space-before-tab,cr-at-eol diff --check

Closes #793