More shinier bubbles; the chat's top edge fades instead of clipping

Bubbles: ten -> eighteen (interleaved, 18px to 96px, 10-23s runs), with a
tighter specular hotspot, a reflected-light glint low on the sphere, a 1px
glass edge and a brighter inner rim on both the bubbles and the drifting
orbs. Bodies stay translucent with capped opacity, so wallpaper text stays
readable; bubble-perf shows no added frame cost.

Chat: the conversation scrolls up to the glass header, and a line clipped
exactly at that edge read as a rendering bug over the busy wallpaper - the
scroller now carries a 14px top mask in Aero, shorter than the column's
16px top padding so a fresh conversation shows no dimming.

Contrast 0 findings, axe clean, chat 101/101, mobile 123/123 (bubble count
pinned to 18), regression 44/44, i18n 13/13, native 33/33.
Version 0.3.7, SW -> freezmo-v66.

components/chat/ChatScreen.tsx

@@ -569,7 +569,7 @@ export function ChatScreen() {
       </header>
 
       <div className="relative min-h-0 flex-1">
-        <div ref={scrollRef} onScroll={onScroll} className="h-full overflow-y-auto overscroll-contain">
+        <div ref={scrollRef} onScroll={onScroll} className="chat-scroll h-full overflow-y-auto overscroll-contain">
           <div className="mx-auto w-full max-w-3xl space-y-4 px-4 py-4">
             {messages.length === 0 ? (
               <div className="space-y-5 py-6">