feat: standardize icon sizes and replace pan icon with UnfoldHorizontal

- Replaced CircleArrowOutUpRight pan icon with UnfoldHorizontal
- Standardized all track control icons to h-3.5 w-3.5:
  - Volume, Pan, Mic, and Gauge icons now have consistent sizing
- Improves visual consistency across the track control panel

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

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

components/tracks/Track.tsx

@@ -1,7 +1,7 @@
 'use client';
 
 import * as React from 'react';
-import { Volume2, VolumeX, Headphones, Trash2, ChevronDown, ChevronRight, CircleArrowOutUpRight, Upload, Plus, Mic, Gauge } from 'lucide-react';
+import { Volume2, VolumeX, Headphones, Trash2, ChevronDown, ChevronRight, UnfoldHorizontal, Upload, Plus, Mic, Gauge } from 'lucide-react';
 import type { Track as TrackType } from '@/types/track';
 import { Button } from '@/components/ui/Button';
 import { Slider } from '@/components/ui/Slider';
@@ -528,7 +528,7 @@ export function Track({
             {/* Pan */}
             <div className="flex items-center gap-2">
               <label className="text-xs text-muted-foreground flex items-center gap-1 w-16 flex-shrink-0">
-                <CircleArrowOutUpRight className="h-3 w-3" />
+                <UnfoldHorizontal className="h-3.5 w-3.5" />
                 Pan
               </label>
               <div className="flex-1">
@@ -554,12 +554,12 @@ export function Track({
               <label className="text-xs text-muted-foreground flex items-center gap-1 w-16 flex-shrink-0">
                 {track.recordEnabled || isRecording ? (
                   <>
-                    <Mic className="h-3 w-3" />
+                    <Mic className="h-3.5 w-3.5" />
                     Input
                   </>
                 ) : (
                   <>
-                    <Gauge className="h-3 w-3" />
+                    <Gauge className="h-3.5 w-3.5" />
                     Level
                   </>
                 )}