feat: implement per-track and master effect chains (Option 3)

Architecture:
- Each track now has its own effect chain stored in track.effectChain
- Separate master effect chain for the final mix output
- SidePanel has 3 tabs: Tracks, Track FX, Master FX

Changes:
- types/track.ts: Add effectChain field to Track interface
- lib/audio/track-utils.ts: Initialize effect chain when creating tracks
- lib/hooks/useMultiTrack.ts: Exclude effectChain from localStorage, recreate on load
- components/editor/AudioEditor.tsx:
  - Add master effect chain state using useEffectChain hook
  - Add handlers for per-track effect chain manipulation
  - Pass both track and master effect chains to SidePanel
- components/layout/SidePanel.tsx:
  - Update to 3-tab interface (Tracks | Track FX | Master FX)
  - Track FX tab shows effects for currently selected track
  - Master FX tab shows master bus effects with preset management
  - Different icons for track vs master effects tabs

Note: Effect processing in Web Audio API not yet implemented.
This commit sets up the data structures and UI.

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

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

types/track.ts

@@ -2,6 +2,8 @@
  * Multi-track types and interfaces
  */
 
+import type { EffectChain } from '@/lib/audio/effects/chain';
+
 export interface Track {
   id: string;
   name: string;
@@ -16,6 +18,9 @@ export interface Track {
   solo: boolean;
   recordEnabled: boolean;
 
+  // Effects
+  effectChain: EffectChain;
+
   // UI state
   collapsed: boolean;
   selected: boolean;