fix: restore automation lanes and effects sections in two-column layout

Restored the automation lane and effects sections that were removed during
the Track component refactoring. These sections now render as full-width
rows below each track, spanning across both the controls and waveforms columns.

Changes:
- Created TrackExtensions component for effects section rendering
- Added automation lane rendering in TrackList after each track waveform
- Added placeholder spacers in left controls column to maintain alignment
- Effects section shows collapsible device rack with mini preview when collapsed
- Automation lanes render when track.automation.showAutomation is true
- Import dialog moved to waveform-only rendering mode

The automation and effects sections are now properly unfoldable again.

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

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

components/tracks/TrackExtensions.tsx

@@ -0,0 +1,128 @@
+'use client';
+
+import * as React from 'react';
+import { Plus, ChevronDown, ChevronRight } from 'lucide-react';
+import type { Track as TrackType } from '@/types/track';
+import { Button } from '@/components/ui/Button';
+import { cn } from '@/lib/utils/cn';
+import { EffectDevice } from '@/components/effects/EffectDevice';
+import { EffectBrowser } from '@/components/effects/EffectBrowser';
+import type { EffectType } from '@/lib/audio/effects/chain';
+
+export interface TrackExtensionsProps {
+  track: TrackType;
+  onUpdateTrack: (trackId: string, updates: Partial<TrackType>) => void;
+  onToggleEffect?: (effectId: string) => void;
+  onRemoveEffect?: (effectId: string) => void;
+  onUpdateEffect?: (effectId: string, parameters: any) => void;
+  onAddEffect?: (effectType: EffectType) => void;
+}
+
+export function TrackExtensions({
+  track,
+  onUpdateTrack,
+  onToggleEffect,
+  onRemoveEffect,
+  onUpdateEffect,
+  onAddEffect,
+}: TrackExtensionsProps) {
+  const [effectBrowserOpen, setEffectBrowserOpen] = React.useState(false);
+
+  // Don't render if track is collapsed
+  if (track.collapsed) {
+    return null;
+  }
+
+  return (
+    <>
+      {/* Effects Section (Collapsible, Full Width) */}
+      <div className="bg-muted/50 border-b border-border/50">
+        {/* Effects Header - clickable to toggle */}
+        <div
+          className="flex items-center gap-2 px-3 py-1.5 cursor-pointer hover:bg-accent/30 transition-colors"
+          onClick={() => {
+            onUpdateTrack(track.id, {
+              showEffects: !track.showEffects,
+            });
+          }}
+        >
+          {track.showEffects ? (
+            <ChevronDown className="h-3.5 w-3.5 text-muted-foreground flex-shrink-0" />
+          ) : (
+            <ChevronRight className="h-3.5 w-3.5 text-muted-foreground flex-shrink-0" />
+          )}
+
+          {/* Show mini effect chain when collapsed */}
+          {!track.showEffects && track.effectChain.effects.length > 0 ? (
+            <div className="flex-1 flex items-center gap-1 overflow-x-auto custom-scrollbar">
+              {track.effectChain.effects.map((effect) => (
+                <div
+                  key={effect.id}
+                  className={cn(
+                    'px-2 py-0.5 rounded text-[10px] font-medium flex-shrink-0',
+                    effect.enabled
+                      ? 'bg-primary/20 text-primary border border-primary/30'
+                      : 'bg-muted/30 text-muted-foreground border border-border'
+                  )}
+                >
+                  {effect.name}
+                </div>
+              ))}
+            </div>
+          ) : (
+            <span className="text-xs font-medium text-muted-foreground">
+              Devices ({track.effectChain.effects.length})
+            </span>
+          )}
+
+          <Button
+            variant="ghost"
+            size="icon-sm"
+            onClick={(e) => {
+              e.stopPropagation();
+              setEffectBrowserOpen(true);
+            }}
+            title="Add effect"
+            className="h-5 w-5 flex-shrink-0"
+          >
+            <Plus className="h-3 w-3" />
+          </Button>
+        </div>
+
+        {/* Horizontal scrolling device rack - expanded state */}
+        {track.showEffects && (
+          <div className="h-48 overflow-x-auto custom-scrollbar bg-muted/70">
+            <div className="flex h-full">
+              {track.effectChain.effects.length === 0 ? (
+                <div className="text-xs text-muted-foreground text-center py-8 w-full">
+                  No devices. Click + to add an effect.
+                </div>
+              ) : (
+                track.effectChain.effects.map((effect) => (
+                  <EffectDevice
+                    key={effect.id}
+                    effect={effect}
+                    onToggleEnabled={() => onToggleEffect?.(effect.id)}
+                    onRemove={() => onRemoveEffect?.(effect.id)}
+                    onUpdateParameters={(params) => onUpdateEffect?.(effect.id, params)}
+                  />
+                ))
+              )}
+            </div>
+          </div>
+        )}
+      </div>
+
+      {/* Effect Browser Dialog */}
+      <EffectBrowser
+        open={effectBrowserOpen}
+        onClose={() => setEffectBrowserOpen(false)}
+        onSelectEffect={(effectType) => {
+          if (onAddEffect) {
+            onAddEffect(effectType);
+          }
+        }}
+      />
+    </>
+  );
+}