Add complete MIDI search and synthesis pipeline

Backend (MVP):
- Express API with /search and /fetch endpoints
- BitMidi and Dongrays search adapters with scoring heuristics
- CORS proxy with disk caching and validation
- Quality assessment and file size limits

Frontend Integration:
- Switch to @tonejs/midi parser for reliable MIDI parsing
- MIDIService for backend API communication
- MotifEngine updated to try real MIDI, fallback to synthetic
- Enhanced error handling and logging

Development:
- Concurrent frontend/backend npm scripts
- Basic project documentation

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

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

server/src/types.ts

@@ -0,0 +1,22 @@
+export interface MIDICandidate {
+  id: string;
+  title: string;
+  source: 'bitmidi' | 'dongrays';
+  pageUrl: string;
+  midiUrl: string;
+  confidence: number;
+  fileSize?: number;
+  duration?: number;
+}
+
+export interface SearchAdapter {
+  name: string;
+  search(query: string): Promise<MIDICandidate[]>;
+}
+
+export interface CacheEntry {
+  hash: string;
+  filename: string;
+  size: number;
+  timestamp: number;
+}