fix: align automation lane with waveform, improve header layout

Automation lane improvements:
- Lane now aligns exactly with waveform width using two-column layout
- Added 180px left spacer to match track controls sidebar
- Playhead marker now aligns perfectly with waveform

Automation header improvements:
- Dropdown has fixed width (min-w-[120px] max-w-[200px]) instead of flex-1
- Eye icon (show/hide) is now positioned absolutely on the right
- Cleaner, more compact header layout

Visual consistency:
- Removed redundant border-b from AutomationLane (handled by parent)
- Automation lane and waveform now perfectly aligned vertically

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

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

components/automation/AutomationLane.tsx

@@ -294,7 +294,7 @@ export function AutomationLane({
   if (!lane.visible) return null;
 
   return (
-    <div className={cn('flex flex-col border-b border-border/50', className)} style={{ height: lane.height + 30 }}>
+    <div className={cn('flex flex-col', className)} style={{ height: lane.height + 30 }}>
       {/* Header */}
       <AutomationHeader
         parameterName={lane.parameterName}