test: cover public library behavior

[rdlabo]

Summary

• add minimum behavioral coverage for the public surfaces of kit, photo-editor, scroll-header, and scroll-strategies
• cover editor/viewer inputs, labels, crop/filter/save/remove/zoom flows, lifecycle cleanup, browser/native file selection, scroll thresholds, virtual-scroll offsets, strategy boundaries, haptics, and component mounting
• use real jsdom behavior where practical and assert side effects and boundary values instead of creation-only smoke tests
• keep the suite free of focused or skipped specs

Bugs exposed and fixed by the tests

• browser photo selection now settles on empty, invalid, aborted, read-failure, and resize-failure paths; the file input is cleared early enough to allow the same file to be selected again
• smooth CDK virtual scrolling now updates only the active viewport orientation, preventing an X offset from overwriting a vertical Y offset

Test totals

Project	Tests
demo	11
photo-editor	33
scroll-header	18
scroll-strategies	42
kit	944
Total	1,048

Verification

• npm run lint
• npm run test
• npm run build
• git diff --check
• no .skip, .only, fit, or fdescribe
• manager review: APPROVE after two fix-and-rereview cycles
• OSS maintainer review: APPROVE after one fix-and-rereview cycle