fix(web): Adjust mobile rainbow glow to avoid green edge (#47)

500% background-size showed too much of the gradient at rest,
revealing green (#bfff80) at the button edge. 650% shows ~15%
of the gradient, landing safely on white while still improving
color visibility during animation.

src/compose_farm/web/static/app.css

@@ -127,5 +127,5 @@
 
 /* Smaller screens: reduce gradient size so more colors are visible */
 @media (max-width: 768px) {
-    #cmd-fab { --bg-size: 500%; }
+    #cmd-fab { --bg-size: 650%; }
 }