task: #3637929 Rebuild the theme assets with Bootstrap 5.3.9

Issue: #3637929

What changed / why

• Bootstrap 5.3.9: .modal-xxl, prefers-reduced-motion for placeholders, the datetime minute-field fix and the tooltip and popover fixes. The Popper global fixer is re-applied. Floor raised to "bootstrap": "^5.3.9".
• bootstrap-borders-utilities pinned to exactly 1.0.2: ^1.0.2 now resolves to 1.0.8, an older 2021 upload without the imported files, so bootstrap.base.css silently fails to compile. The lockfile removed in #3635499 had held it at 1.0.2.
• Most of the CSS diff is sass 1.102+ writing mixed colours as percentages. Same colours; sass stays unpinned.
• Bootstrap Icons refreshed to 1.13.2 by theme:init.
• Second commit pins stylelint-prettier to 5.0.3. With the borders fix bootstrap.base.css compiles again, and stylelint --fix on it never finishes with 5.1.0, so theme:full-build hangs. Same pin as Horizon Aid #3636458, Educare and Rightup. A full build with 5.0.3 reproduces the committed CSS unchanged.

AI-Generated: Yes

Checkpoints:

• File an issue
• Addition/Change/Update/Fix
• Testing to ensure no regression
• Automated unit testing coverage
• Automated functional testing coverage
• UX/UI designer responsibilities
• Readability
• Accessibility
• Performance
• Security
• Developer Documentation
• User Guide Documentation
• Reviewed by human
• Code review by maintainers
• Full testing and approval
• Credit contributors
• Review with the product owner
• Release notes snippet
• Release