Add MIDIUtil examples with working 90s dance compositions

- 01-basic-chord.py: chord progressions (C major)
- 02-90s-dance-track.py: 5-track 90s dance (arp, bass, pads, drums, piano)
- 03-arpeggiator.py: reusable arpeggio generator with dir/type options
- 04-single-note.py: minimal single-note example
- Rewrite compose_neon_dreams.py: cleaner track functions, proper velocity=0 note_off, tick helper
- Add README.md with setup and API reference

Uses MIDIUtil library (beats-based API) instead of mido
(clocks-based API)

examples/03-arpeggiator.py

@@ -0,0 +1,119 @@
+#!/usr/bin/env python3
+"""
+03-arpeggiator.py - MIDIUtil arpeggiator
+Generates automatic ascending/descending arpeggios from chord sets.
+Shows clean patterns using MIDIUtil's beat-based time API.
+"""
+from midiutil import MIDIFile
+
+# ==============================
+# Configuration
+# ==============================
+BPM = 132
+PPQ = 960
+
+# Chord definitions: (root MIDI note, number of beats)
+# Using A minor progression: Am | F | G | E
+CHORDS = [
+    {"root": 57, "beats": 4},   # Am  (A3)
+    {"root": 53, "beats": 4},   # F   (F3)
+    {"root": 55, "beats": 4},   # G   (G3)
+    {"root": 52, "beats": 4},   # E   (E3)
+]
+
+# Arpeggio patterns: semitone intervals from chord root
+CHORD_TYPES = {
+    "major":  [0, 4, 7, 12],         # Major triad + octave
+    "minor":  [0, 3, 7, 12],         # Minor triad + octave
+    "dim":    [0, 3, 6, 9],          # Diminished
+    "aug":    [0, 4, 8, 12],         # Augmented
+}
+
+# ==============================
+# Helper function
+# ==============================
+def make_arpeggio(midi, track, channel, chord_list,
+                  arp_type="minor", arp_direction="up",
+                  subdivisions=4, volume=90):
+    """
+    Generate an arpeggio track from a chord list.
+    
+    Args:
+        midi: MIDIFile object
+        track: track index (int)
+        channel: MIDI channel (int, 0-15)
+        chord_list: list of {"root": M, "beats": N} with MIDI root notes
+        arp_type: chord type key for CHORD_TYPES dict ("minor", "major", etc.)
+        arp_direction: "up" or "down" for arpeggio direction
+        subdivisions: 16th-note speed (4 = standard 16ths, 8 = 32nds)
+        volume: note velocity (0-127)
+    """
+    notes = CHORD_TYPES[arp_type].copy()
+    if arp_direction == "down":
+        notes = notes[::-1]
+    
+    note_beats = 1.0 / subdivisions  # duration per arpeggio hit
+    
+    beat = 0.0
+    for chord in chord_list:
+        root = chord["root"]
+        chord_duration = chord["beats"]
+        
+        total_hits = int(chord_duration / note_beats)
+        for i in range(total_hits):
+            note_idx = i % len(notes)
+            octave = i // len(notes)
+            pitch = root + notes[note_idx] + (octave * 12)
+            
+            # Cap MIDI pitch range
+            pitch = max(0, min(127, pitch))
+            
+            midi.addNote(track, channel, pitch, beat, note_beats, volume)
+            beat += note_beats
+
+
+# ==============================
+# Create multi-track file
+# ==============================
+midi = MIDIFile(3, file_format=1, ticks_per_quarternote=PPQ)
+midi.addTempo(0, 0, BPM)
+midi.addTrackName(0, 0, "Arpeggio Lead 1 (Minor)")
+midi.addTrackName(1, 0, "Arpeggio Lead 2 (Major)")
+midi.addTrackName(2, 0, "Bass")
+
+# Track 0: Upward minor arpeggio (GM 80 - Lead 1 Synth)
+midi.addProgramChange(0, 0, 0, 80)
+make_arpeggio(midi, 0, 0, CHORDS,
+              arp_type="minor", arp_direction="up",
+              subdivisions=4, volume=85)
+
+# Track 1: Descending major arpeggio (GM 84 - Lead 3 Synth)
+midi.addProgramChange(1, 0, 0, 84)
+make_arpeggio(midi, 1, 0, CHORDS,
+              arp_type="major", arp_direction="down",
+              subdivisions=8, volume=80)
+
+# Track 2: Bass follows chord roots (quarter notes)
+midi.addProgramChange(2, 0, 0, 37)  # Synth Bass 1
+for chord in CHORDS:
+    root = chord["root"]
+    chord_duration = chord["beats"]
+    
+    # Two quarter-note pulses per beat
+    for beat_offset in range(0, int(chord_duration * 2)):
+        time = beat_offset * 0.5
+        midi.addNote(2, 0, root, time, 0.4, 100)
+        # Octave pulse for depth
+        octave = root + 12
+        if octave <= 127:
+            midi.addNote(2, 0, octave, time, 0.2, 80)
+
+
+# ==============================
+# Write to Disk
+# ==============================
+with open("arpeggiator.mid", "wb") as output_file:
+    midi.writeFile(output_file)
+
+print("Written: arpeggiator.mid")
+print("  3-track arpeggio piece with minor/major contrast")