fix: use absolute positioning for hidden AgentInputArea to prevent layout space

AgentInputArea was still taking up 88px height when opacity was 0, creating
a gap between status bar and realtime controls. Now switches to position
absolute when hidden (opacity < 0.5) to remove from layout flow completely.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

packages/app/src/components/agent-input-area.tsx

@@ -36,6 +36,8 @@ export function AgentInputArea({ agentId, isRealtimeMode }: AgentInputAreaProps)
   const animatedStyle = useAnimatedStyle(() => {
     return {
       opacity: opacity.value,
+      // When hidden, use absolute positioning to remove from layout flow
+      position: opacity.value < 0.5 ? ("absolute" as const) : ("relative" as const),
       // When hidden, disable pointer events so GlobalFooter's controls are interactive
       pointerEvents: opacity.value < 0.5 ? ("none" as const) : ("auto" as const),
     };