refactor: single automation lane with parameter dropdown and fixed-height effects panel

Phase 9 Automation Improvements:
- Replaced multiple automation lanes with single lane + parameter selector
- Added dropdown in automation header to switch between parameters:
  - Track parameters: Volume, Pan
  - Effect parameters: Dynamically generated from effect chain
- Lanes are created on-demand when parameter is selected
- Effects panel now has fixed height (280px) with scroll
  - Panel no longer resizes when effects are expanded
  - Maintains consistent UI layout

Technical changes:
- Track.automation.selectedParameterId: Tracks current parameter
- AutomationHeader: Added parameter dropdown props
- AutomationLane: Passes parameter selection to header
- Track.tsx: Single lane rendering with IIFE for parameter list
- Effects panel: h-[280px] with flex layout and overflow-y-auto

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

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

types/track.ts

@@ -27,6 +27,7 @@ export interface Track {
   automation: {
     lanes: AutomationLane[];
     showAutomation: boolean; // Master show/hide toggle
+    selectedParameterId?: string; // Currently selected parameter to display
   };
 
   // UI state