Implement complete search results + dual player UI

Backend Enhancements:
- Add ParsedMIDIInfo with track analysis and quality issues
- New /api/midi/parse endpoint for MIDI metadata extraction
- Enhanced MIDIService with parseMIDI method

MIDI Preview Player:
- Complete MIDIPlayer class with polyphonic playback
- Basic oscillator mapping (bass=square, mid=triangle, high=sine)
- Lookahead scheduling with proper cleanup
- Automatic stopping when MIDI ends

New UI Flow:
1. Search → Results table with metadata
2. Select MIDI → Shows parsed info (duration, tracks, tempo)
3. Dual transport: Preview Original vs Generate Motif
4. Try Next Result button for easy A/B testing

Search Results Table:
- Title, source, confidence bar, duration, track count
- Quality issues display (short duration, few notes, etc.)
- Auto-select best result, manual selection available
- Visual confidence bars and issue warnings

This makes the project feel "real" - you can now:
- See exactly what MIDI was found
- Verify it's the right song via preview
- Compare original vs procedural synthesis
- Easily try different results

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

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

server/src/types.ts

@@ -7,6 +7,25 @@ export interface MIDICandidate {
   confidence: number;
   fileSize?: number;
   duration?: number;
+  parsed?: ParsedMIDIInfo;
+}
+
+export interface ParsedMIDIInfo {
+  durationSec: number;
+  tempoBpm: number;
+  timeSig?: { num: number; den: number };
+  tracks: TrackInfo[];
+  noteCount: number;
+  issues: string[];
+}
+
+export interface TrackInfo {
+  id: number;
+  name?: string;
+  program?: number;
+  noteCount: number;
+  channel?: number;
+  register: 'low' | 'mid' | 'high';
 }
 
 export interface SearchAdapter {