Blend the liquid drop into its card and let it be spun by hand

The rim hue drifted with play time until it left the card's colour altogether, so a
pink card could carry a green drop. It now only sways around the accent. The edge
fades into the page, a halo in the accent pulses behind it like the plain artwork's
glow, the surface reflects the accent from above, and the title and the rest of the
card sit on top where the drop spills over them.

Dragging the drop turns it (sideways only on touch, where up and down turn the page).
A flick keeps it spinning; it slows down and a weak spring wobbles it back to face the
front. Spun fast it flattens a little and sloshes, and the artwork blurs into colour
where it is seen from the side. A spin is not a tap, so it does not pause.

README.md

@@ -159,8 +159,9 @@ Single-letter keys clash with vim-key browser extensions (Vimium and the like),
 - `blob/`: the liquid artwork. One WebGL2 canvas moves into the playing card: an icosphere
   displaced by noise driven by those features (lobes, ripples, snare spikes, a ring after each
   kick), showing the artwork through its surface. Tempo, tags and key set its character
-  (`blob/style.ts`). It steps its quality down on slow devices and falls back to the plain
-  artwork without WebGL2, with reduced motion, or with visuals set to simple.
+  (`blob/style.ts`). Dragging it spins it; a flick keeps spinning and springs back to face
+  the front (`blob/spin.ts`). It steps its quality down on slow devices and falls back to the
+  plain artwork without WebGL2, with reduced motion, or with visuals set to simple.
 - `visual.ts`: runs both per frame, plus `--energy` (kick-driven) for the CSS glow.
 - `station.ts`: the radio sheet.
 - `color.ts`: each card's accent colour (`--card-accent`) from the artist image.