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>

components/automation/AutomationLane.tsx

@@ -16,6 +16,10 @@ export interface AutomationLaneProps {
   onUpdatePoint?: (pointId: string, updates: Partial<AutomationPointType>) => void;
   onRemovePoint?: (pointId: string) => void;
   className?: string;
+  // Parameter selection
+  availableParameters?: Array<{ id: string; name: string }>;
+  selectedParameterId?: string;
+  onParameterChange?: (parameterId: string) => void;
 }
 
 export function AutomationLane({
@@ -28,6 +32,9 @@ export function AutomationLane({
   onUpdatePoint,
   onRemovePoint,
   className,
+  availableParameters,
+  selectedParameterId,
+  onParameterChange,
 }: AutomationLaneProps) {
   const canvasRef = React.useRef<HTMLCanvasElement>(null);
   const containerRef = React.useRef<HTMLDivElement>(null);
@@ -302,6 +309,9 @@ export function AutomationLane({
           onUpdateLane?.({ height: newHeight });
         }}
         formatter={lane.valueRange.formatter}
+        availableParameters={availableParameters}
+        selectedParameterId={selectedParameterId}
+        onParameterChange={onParameterChange}
       />
 
       {/* Lane canvas area */}