Updates `profile-modal.html` and `application-form.html` to use root-relative paths for images and iframes, fixing 404 errors in E2E tests. Adds a preflight check to `tests/e2e/ui-modals.spec.ts` to verify asset availability.
- Replaced raw pixel value in `css/tailwind.source.css` with theme-based `calc()` to fix token lint error.
- Updated `tests/e2e/ui-modals.spec.ts` to skip close control check for `lockdown-modal`, aligning with inescapable design.
- Added `KNOWN_ISSUES.md` documenting unresolved visual regression in sidebar layout and moderation UI rendering issues in tests.
- Reverted incomplete attempt to fix sidebar CSS logic to maintain stability.