refactor: migrate from FL Studio to REAPER with rpp library

Replace FL Studio binary .flp output with REAPER text-based .rpp output
using the rpp Python library (Perlence/rpp).

- Add core/schema.py: DAW-agnostic data types (SongDefinition, TrackDef,
  ClipDef, MidiNote, PluginDef)
- Add reaper_builder/: RPP file generation via rpp.Element + headless
  render via reaper.exe CLI
- Add composer/converters.py: bridge rhythm.py/melodic.py note dicts
  to core.schema MidiNote objects
- Rewrite scripts/compose.py: real generator pipeline with --render flag
- Delete src/flp_builder/, src/scanner/, mcp/, flstudio-mcp/, old scripts
- Add 40 passing tests (schema, builder, converters, compose, render)

tests/test_core_schema.py

@@ -0,0 +1,137 @@
+"""Tests for src/core/schema.py — SongDefinition, TrackDef, ClipDef, MidiNote."""
+
+import sys
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).parents[1]))
+
+import pytest
+from src.core.schema import SongDefinition, SongMeta, TrackDef, ClipDef, MidiNote
+
+
+class TestSongDefinitionInstantiation:
+    """Test SongDefinition instantiation with valid data."""
+
+    def test_song_definition_with_valid_data(self):
+        """SongDefinition instantiates with meta and tracks."""
+        meta = SongMeta(bpm=95, key="Am", title="Test Song")
+        song = SongDefinition(meta=meta, tracks=[])
+        assert song.meta.bpm == 95
+        assert song.meta.key == "Am"
+        assert song.meta.title == "Test Song"
+        assert song.tracks == []
+
+    def test_song_definition_with_multiple_tracks(self):
+        """SongDefinition accepts multiple TrackDef entries."""
+        meta = SongMeta(bpm=95, key="Am")
+        track1 = TrackDef(name="Kick", volume=0.85)
+        track2 = TrackDef(name="Bass", volume=0.80)
+        song = SongDefinition(meta=meta, tracks=[track1, track2])
+        assert len(song.tracks) == 2
+        assert song.tracks[0].name == "Kick"
+        assert song.tracks[1].name == "Bass"
+
+
+class TestTrackDefWithAudioClip:
+    """Test TrackDef with audio clip (sample_path)."""
+
+    def test_track_with_audio_clip(self):
+        """TrackDef with audio clip has audio_path set."""
+        clip = ClipDef(
+            position=0.0,
+            length=16.0,
+            name="Kick Loop",
+            audio_path="C:/samples/kick.wav",
+        )
+        track = TrackDef(name="Drums", clips=[clip])
+        assert len(track.clips) == 1
+        assert track.clips[0].is_audio
+        assert track.clips[0].audio_path == "C:/samples/kick.wav"
+        assert not track.clips[0].is_midi
+
+    def test_track_with_multiple_audio_clips(self):
+        """TrackDef can hold multiple audio clips."""
+        clip1 = ClipDef(position=0.0, length=16.0, audio_path="C:/samples/kick.wav")
+        clip2 = ClipDef(position=16.0, length=16.0, audio_path="C:/samples/kick2.wav")
+        track = TrackDef(name="Drums", clips=[clip1, clip2])
+        assert len(track.clips) == 2
+        assert track.clips[0].audio_path == "C:/samples/kick.wav"
+        assert track.clips[1].audio_path == "C:/samples/kick2.wav"
+
+
+class TestClipDefWithMidiNotes:
+    """Test ClipDef with MIDI notes."""
+
+    def test_clip_with_midi_notes(self):
+        """ClipDef with midi_notes is identified as MIDI clip."""
+        note = MidiNote(pitch=36, start=0.0, duration=1.0, velocity=100)
+        clip = ClipDef(
+            position=0.0,
+            length=16.0,
+            name="Kick Pattern",
+            midi_notes=[note],
+        )
+        assert clip.is_midi
+        assert not clip.is_audio
+        assert len(clip.midi_notes) == 1
+        assert clip.midi_notes[0].pitch == 36
+
+    def test_clip_with_multiple_midi_notes(self):
+        """ClipDef can hold multiple MidiNote entries."""
+        notes = [
+            MidiNote(pitch=36, start=0.0, duration=0.25, velocity=115),
+            MidiNote(pitch=36, start=1.5, duration=0.25, velocity=105),
+            MidiNote(pitch=38, start=2.0, duration=0.15, velocity=100),
+        ]
+        clip = ClipDef(position=0.0, length=16.0, name="Drum Pattern", midi_notes=notes)
+        assert len(clip.midi_notes) == 3
+        assert clip.midi_notes[0].pitch == 36
+        assert clip.midi_notes[1].pitch == 36
+        assert clip.midi_notes[2].pitch == 38
+
+
+class TestValidationNegativeBPM:
+    """Test validation: negative BPM raises ValueError."""
+
+    def test_negative_bpm_raises_value_error(self):
+        """SongDefinition.validate() returns error for negative BPM."""
+        meta = SongMeta(bpm=-10, key="Am")
+        song = SongDefinition(meta=meta, tracks=[])
+        errors = song.validate()
+        assert any("bpm" in e.lower() for e in errors)
+
+    def test_zero_bpm_raises_value_error(self):
+        """SongDefinition.validate() returns error for zero BPM."""
+        meta = SongMeta(bpm=0, key="Am")
+        song = SongDefinition(meta=meta, tracks=[])
+        errors = song.validate()
+        assert any("bpm" in e.lower() for e in errors)
+
+    def test_valid_bpm_passes(self):
+        """SongDefinition.validate() passes for BPM 20-999."""
+        meta = SongMeta(bpm=95, key="Am")
+        song = SongDefinition(meta=meta, tracks=[])
+        errors = song.validate()
+        assert not any("bpm" in e.lower() for e in errors)
+
+
+class TestMidiNote:
+    """Test MidiNote dataclass."""
+
+    def test_midi_note_defaults(self):
+        """MidiNote has sensible defaults for velocity."""
+        note = MidiNote(pitch=60, start=0.0, duration=1.0)
+        assert note.pitch == 60
+        assert note.start == 0.0
+        assert note.duration == 1.0
+        assert note.velocity == 64  # default
+
+    def test_midi_note_explicit_velocity(self):
+        """MidiNote accepts explicit velocity."""
+        note = MidiNote(pitch=60, start=0.0, duration=1.0, velocity=127)
+        assert note.velocity == 127
+
+    def test_midi_note_velocity_clamping(self):
+        """MidiNote does NOT clamp — accepts any int (caller's responsibility)."""
+        note = MidiNote(pitch=60, start=0.0, duration=1.0, velocity=200)
+        assert note.velocity == 200