Add public showcase case pages

[huangruiteng]

Summary

• add bilingual public showcase index and case HTML pages for the approved showcase set
• keep the canonical hardware Chinese HTML page untouched while adding an English companion
• generate the pages from docs/showcases/showcase-catalog.json via examples/showcase-html-pages.py
• update showcase catalog, animation storyboard/prototype, bundle copy logic, and focused smokes

Validation

• python3 examples/showcase-html-pages.py --check
• python3 examples/showcase-catalog-smoke.py
• node examples/frontstage-share-bundle-smoke.mjs
• python3 examples/showcase-frontstage-prototype-smoke.py
• python3 examples/showcase-animation-source-boundary-smoke.py
• python3 examples/showcase-animation-prototype-smoke.py
• python3 -m py_compile examples/showcase-html-pages.py examples/showcase-animation-prototype.py examples/showcase-catalog-smoke.py examples/showcase-frontstage-prototype.py examples/showcase-frontstage-prototype-smoke.py examples/showcase-animation-source-boundary-smoke.py examples/showcase-animation-prototype-smoke.py
• git diff --check origin/main...HEAD
• loopx check --scan-path docs/showcases --scan-path examples/showcase-html-pages.py --scan-path examples/showcase-catalog-smoke.py --scan-path examples/showcase-frontstage-prototype.py --scan-path examples/showcase-frontstage-prototype-smoke.py --scan-path examples/showcase-animation-source-boundary-smoke.py --scan-path examples/showcase-animation-prototype.py --scan-path examples/showcase-animation-prototype-smoke.py --scan-path examples/export-frontstage-share-bundle.mjs --scan-path examples/frontstage-share-bundle-smoke.mjs

Boundary

• public docs/examples only; no .local, run history, credentials, raw logs, or local state
• private-marker scan hits were expected boundary text and smoke sentinels only
• not a Lark Kanban change