perf(sprites): ship 192px sprites and a manifest of every sprite

Sprites were shipped at 512x512 but render at 44-64px in the box grid.
Resizing to 192px halves each file (median 15.5KB -> 7.6KB); a full dex
of artwork drops from 16.6MB to 7.6MB.

The sprite build now also writes static/sprites-small/manifest.json,
listing every sprite (all forms, shiny and female variants) with its
size, so the offline worker can save the complete set and report what
is missing. A unit test keeps it in step with the files on disk.

.prettierignore

@@ -9,6 +9,7 @@ src/lib/helpers/pokeapi-pokemon.json
 static/sprites/pokemon.json
 src/lib/helpers/pokedex.json
 src/lib/helpers/sprites.json
+static/sprites-small/manifest.json
 
 # Machine-local editor and tool settings.
 **/*.local.json