The old favicon/logo were pinned by `Cache-Control: immutable` (1 year), so
browsers never refetched the new glass-bloom mark.
- _headers: favicon.ico + icon.png now cache for a day (revalidating), not
immutable; drop dead /screenshots + /assets rules; cache /images for a week
- version icon references (?v=2) so existing immutable caches are busted now
- add a modern PNG icon link (/icon.png) that browsers prefer over the .ico
- remove the dead root _headers duplicate (only public/_headers ships)
ZacharyZhang-NY
52937c6c88
