feat: ship a web app manifest and home-screen icons

Adding the app to a phone home screen produced a blank tile: index.html
linked only an SVG favicon, and Safari ignores SVG for apple-touch-icon,
substituting a screenshot of the page. There was no manifest at all, so
Android had nothing to install against either.

Generate the rasters from public/logo.svg with sharp, which the repo
already carries. The output is committed so a plain `vite build` needs no
image toolchain; re-run scripts/generate-icons.mjs after changing the
logo. The logo's viewBox is wider than it is tall, so each icon centres
the mark on a square #0a0a0f canvas rather than stretching it, inset to
78% normally and 54% for the maskable variant to survive Android's
circular crop.

The SVG favicon stays as the browser tab icon.

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+- Ship a web app manifest and raster home-screen icons, so adding the app to a
+  phone home screen or installing it on desktop uses the God's Eye View mark
+  instead of a blank tile. The icons are generated from `public/logo.svg` by
+  `node scripts/generate-icons.mjs` and committed, so a plain `vite build` needs
+  no image toolchain. The existing SVG favicon still serves the browser tab.
+
 - GBFS v3 station names use English translations when available, then the first
   usable translation or short name. Empty or malformed names no longer appear as
   `[object Object]` or interrupt station loading; legacy string names remain