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_converters.py

@@ -0,0 +1,95 @@
+"""Tests for src/composer/converters.py — rhythm_to_midi, melodic_to_midi."""
+
+import sys
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).parents[1]))
+
+import pytest
+from src.composer.converters import rhythm_to_midi, melodic_to_midi
+from src.core.schema import MidiNote
+
+
+class TestRhythmToMidi:
+    """Tests for rhythm_to_midi() — channel → GM pitch mapping."""
+
+    def test_rhythm_to_midi_kick_channel(self):
+        """Channel 11 (kick) maps to pitch 36 with correct start/duration/velocity."""
+        note_dict = {
+            11: [
+                {"pos": 0.0, "len": 0.25, "key": 36, "vel": 115},
+                {"pos": 1.0, "len": 0.25, "key": 36, "vel": 100},
+            ]
+        }
+        result = rhythm_to_midi(note_dict)
+
+        assert len(result) == 2
+        # Pitch is resolved from CHANNEL_PITCH, not from the dict's "key"
+        assert result[0].pitch == 36
+        assert result[0].start == 0.0
+        assert result[0].duration == 0.25
+        assert result[0].velocity == 115
+
+        assert result[1].pitch == 36
+        assert result[1].start == 1.0
+        assert result[1].duration == 0.25
+        assert result[1].velocity == 100
+
+    def test_rhythm_to_midi_hihat_channel(self):
+        """Channel 15 (hihat) maps to pitch 42."""
+        note_dict = {15: [{"pos": 0.0, "len": 0.125, "key": 42, "vel": 90}]}
+        result = rhythm_to_midi(note_dict)
+
+        assert len(result) == 1
+        assert result[0].pitch == 42
+        assert result[0].start == 0.0
+        assert result[0].duration == 0.125
+        assert result[0].velocity == 90
+
+    def test_rhythm_to_midi_unknown_channel(self):
+        """Unknown channel (not in CHANNEL_PITCH) defaults to pitch 60."""
+        note_dict = {99: [{"pos": 0.0, "len": 0.25, "key": 60, "vel": 100}]}
+        result = rhythm_to_midi(note_dict)
+
+        assert len(result) == 1
+        assert result[0].pitch == 60  # default fallback
+        assert result[0].start == 0.0
+
+    def test_rhythm_to_midi_multi_channel(self):
+        """3 different channels return a flat list with all notes combined."""
+        note_dict = {
+            11: [{"pos": 0.0, "len": 0.25, "key": 36, "vel": 115}],
+            15: [{"pos": 0.5, "len": 0.125, "key": 42, "vel": 90}],
+            10: [{"pos": 1.0, "len": 0.25, "key": 39, "vel": 80}],
+        }
+        result = rhythm_to_midi(note_dict)
+
+        assert len(result) == 3
+        pitches = {n.pitch for n in result}
+        assert pitches == {36, 42, 39}
+
+
+class TestMelodicToMidi:
+    """Tests for melodic_to_midi() — key field used directly as pitch."""
+
+    def test_melodic_to_midi_uses_key_as_pitch(self):
+        """key=60 → pitch 60 (key field is used directly, not mapped)."""
+        note_list = [
+            {"pos": 0.0, "len": 0.5, "key": 60, "vel": 100},
+            {"pos": 0.5, "len": 0.5, "key": 64, "vel": 90},
+            {"pos": 1.0, "len": 0.5, "key": 67, "vel": 95},
+        ]
+        result = melodic_to_midi(note_list)
+
+        assert len(result) == 3
+        assert result[0].pitch == 60
+        assert result[1].pitch == 64
+        assert result[2].pitch == 67
+        assert result[0].start == 0.0
+        assert result[0].duration == 0.5
+        assert result[0].velocity == 100
+
+    def test_melodic_to_midi_empty_list(self):
+        """Empty list returns empty list."""
+        result = melodic_to_midi([])
+        assert result == []