fix: project loading and add editable project name

Fixed project loading to restore all track properties and added inline
project name editing in header.

**AudioEditor.tsx:**
- Added `loadTracks` from useMultiTrack hook
- Fixed `handleLoadProject` to use `loadTracks()` instead of recreating tracks
  - Now properly restores all track properties (effects, automation, volume, pan, etc.)
  - Shows track count in success toast message
- Added editable project name input in header
  - Positioned between logo and track actions
  - Auto-sizes based on text length
  - Saves on blur (triggers auto-save)
  - Smooth hover/focus transitions
  - Muted color that brightens on interaction

**useMultiTrack.ts:**
- Added `loadTracks()` method to replace all tracks at once
- Enables proper project loading with full state restoration
- Maintains all track properties during load

**Fixes:**
- Projects now load correctly with all tracks and their audio buffers
- Track properties (effects, automation, volume, pan, etc.) fully restored
- Project name can be edited inline in header
- Auto-save triggers when project name changes

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

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

lib/hooks/useMultiTrack.ts

@@ -120,6 +120,10 @@ export function useMultiTrack() {
     );
   }, []);
 
+  const loadTracks = useCallback((tracksToLoad: Track[]) => {
+    setTracks(tracksToLoad);
+  }, []);
+
   return {
     tracks,
     addTrack,
@@ -129,5 +133,6 @@ export function useMultiTrack() {
     clearTracks,
     reorderTracks,
     setTrackBuffer,
+    loadTracks,
   };
 }