feat: enhance mobile responsiveness with collapsible controls and automation/effects bars

Added comprehensive mobile support for Phase 15 (Polish & Optimization):

**Mobile Layout Enhancements:**
- Track controls now collapsible on mobile with two states:
  - Collapsed: minimal controls with expand chevron, R/M/S buttons, horizontal level meter
  - Expanded: full height fader, pan control, all buttons
- Track collapse buttons added to mobile view (left chevron for track collapse, right chevron for control collapse)
- Master controls collapse button hidden on desktop (lg:hidden)
- Automation and effects bars now available on mobile layout
- Both bars collapsible with eye/eye-off icons, horizontally scrollable when zoomed
- Mobile vertical stacking: controls → waveform → automation → effects per track

**Bug Fixes:**
- Fixed track controls and waveform container height matching on desktop
- Fixed Modal component prop: isOpen → open in all dialog components
- Fixed TypeScript null check for audioBuffer.duration
- Fixed keyboard shortcut category: 'help' → 'view'

**Technical Improvements:**
- Consistent height calculation using trackHeight variable
- Proper responsive breakpoints with Tailwind (sm:640px, lg:1024px)
- Progressive disclosure pattern for mobile controls

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

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

lib/audio/decoder.ts

@@ -3,6 +3,7 @@
  */
 
 import { getAudioContext } from './context';
+import { checkFileMemoryLimit, type MemoryCheckResult } from '../utils/memory-limits';
 
 export interface ImportOptions {
   convertToMono?: boolean;
@@ -248,6 +249,15 @@ export function isSupportedAudioFormat(file: File): boolean {
          /\.(wav|mp3|ogg|webm|flac|aac|m4a|aiff|aif)$/i.test(file.name);
 }
 
+/**
+ * Check memory requirements for an audio file before decoding
+ * @param file File to check
+ * @returns Memory check result with warning if file is large
+ */
+export function checkAudioFileMemory(file: File): MemoryCheckResult {
+  return checkFileMemoryLimit(file.size);
+}
+
 /**
  * Format duration in seconds to MM:SS format
  */