Nginx was serving css with `expires 1y; Cache-Control: public, immutable`,
which combined with version-less <link href="styles-rest.css"> meant every
browser permanently pinned whatever stylesheet it cached first. Users were
seeing pre-polish-round-2 CSS even after the new image was deployed —
the calendar grid rendered as a vertical stack of weekday names because
the .cal-* rules didn't exist in the cached file.
Move css into the same bucket as js: must-revalidate via ETag. Fonts,
icons, and raster assets stay in the immutable 1y bucket since they don't
change between deploys.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
