feat(ui): complete layout redesign — three-panel desk layout

Replaced the hero + scrollable grid with a fixed-height three-column
workspace:
- Left (fixed 288px): Kira avatar + compact chat + text input
- Center (flex): Large focus timer + notes
- Right (fixed 256px): Music, white noise, wardrobe, pets

Thin top bar: scene selector dots + clock
Thin bottom bar: status + connection indicator

No cards, no scrollable grid, no wasted space. Clean, modern,
everything visible at once. Avatar fills full sidebar height.

frontend/src/components/KiraAvatar.tsx

@@ -197,7 +197,7 @@ export default function KiraAvatar(props: Props) {
   `;
 
   return (
-    <div className="flex flex-col items-center w-full overflow-hidden" style={{ minHeight: '33vh' }}>
+    <div className="flex flex-col items-center w-full h-full overflow-hidden">
       <div className="relative w-full flex-1" style={{ minHeight: 250 }}>
         <div
           ref={canvasRef}