Feature a curated poem selection at the top

[marsrobertson]

Summary

• add a five-poem favourites section above the full archive
• give the lead pick a distinct but restrained visual treatment
• generate every featured card from the canonical plain-text collection
• keep the archive count in sync during rebuilds

Verification

• ran python3 build.py twice and confirmed identical output
• ran python3 -m py_compile build.py
• ran git diff --check
• checked desktop and 390px layouts in-browser; 5 featured cards and all 97 archive cards render with no console warnings or errors