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/AutomationHeader.tsx

@@ -17,6 +17,10 @@ export interface AutomationHeaderProps {
   onHeightChange?: (delta: number) => void;
   className?: string;
   formatter?: (value: number) => string;
+  // Parameter selection
+  availableParameters?: Array<{ id: string; name: string }>;
+  selectedParameterId?: string;
+  onParameterChange?: (parameterId: string) => void;
 }
 
 const MODE_LABELS: Record<AutomationMode, string> = {
@@ -44,6 +48,9 @@ export function AutomationHeader({
   onHeightChange,
   className,
   formatter,
+  availableParameters,
+  selectedParameterId,
+  onParameterChange,
 }: AutomationHeaderProps) {
   const modes: AutomationMode[] = ['read', 'write', 'touch', 'latch'];
   const currentModeIndex = modes.indexOf(mode);
@@ -74,10 +81,24 @@ export function AutomationHeader({
         />
       )}
 
-      {/* Parameter name */}
-      <span className="text-xs font-medium text-foreground flex-1 min-w-0 truncate">
-        {parameterName}
-      </span>
+      {/* Parameter name / selector */}
+      {availableParameters && availableParameters.length > 1 ? (
+        <select
+          value={selectedParameterId}
+          onChange={(e) => onParameterChange?.(e.target.value)}
+          className="text-xs font-medium text-foreground flex-1 min-w-0 bg-background/50 border border-border/30 rounded px-1.5 py-0.5 hover:bg-background/80 focus:outline-none focus:ring-1 focus:ring-primary"
+        >
+          {availableParameters.map((param) => (
+            <option key={param.id} value={param.id}>
+              {param.name}
+            </option>
+          ))}
+        </select>
+      ) : (
+        <span className="text-xs font-medium text-foreground flex-1 min-w-0 truncate">
+          {parameterName}
+        </span>
+      )}
 
       {/* Current value display */}
       {currentValue !== undefined && (

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 */}