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_render_cli.py

@@ -0,0 +1,127 @@
+"""Tests for scripts/compose.py render CLI flags."""
+
+import sys
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).parents[1]))
+
+import pytest
+import argparse
+from unittest.mock import patch, MagicMock
+from scripts.compose import main as compose_main
+
+
+class TestRenderFlag:
+    """Test --render and --render-output CLI arguments."""
+
+    def test_render_flag_defaults_to_false(self):
+        """Without --render, the render flag should be False."""
+        parser = argparse.ArgumentParser()
+        parser.add_argument("--render", action="store_true")
+        parser.add_argument("--render-output", default=None)
+
+        args = parser.parse_args([])
+        assert args.render is False
+
+    def test_render_flag_true_when_provided(self):
+        """With --render, the flag should be True."""
+        parser = argparse.ArgumentParser()
+        parser.add_argument("--render", action="store_true")
+        parser.add_argument("--render-output", default=None)
+
+        args = parser.parse_args(["--render"])
+        assert args.render is True
+
+    def test_render_output_defaults_to_none(self):
+        """--render-output defaults to None when not provided."""
+        parser = argparse.ArgumentParser()
+        parser.add_argument("--render", action="store_true")
+        parser.add_argument("--render-output", default=None)
+
+        args = parser.parse_args([])
+        assert args.render_output is None
+
+    @patch("scripts.compose.render_project")
+    @patch("scripts.compose.RPPBuilder")
+    def test_render_triggers_render_project_call(self, mock_builder_cls, mock_render):
+        """Calling main with --render invokes render_project."""
+        mock_builder = MagicMock()
+        mock_builder_cls.return_value = mock_builder
+
+        with patch("scripts.compose.SampleSelector") as mock_selector:
+            mock_sel_instance = MagicMock()
+            mock_sel_instance.select_one.return_value = None
+            mock_selector.return_value = mock_sel_instance
+
+            with patch("sys.argv", ["compose.py", "--genre", "reggaeton", "--render"]):
+                compose_main()
+
+        mock_render.assert_called_once()
+        call_args = mock_render.call_args
+        # First arg should be the .rpp path, second should be .wav path
+        rpp_path = call_args[0][0]
+        wav_path = call_args[0][1]
+        assert rpp_path.endswith(".rpp")
+        assert wav_path.endswith(".wav")
+
+    @patch("scripts.compose.render_project")
+    @patch("scripts.compose.RPPBuilder")
+    def test_without_render_does_not_call_render_project(self, mock_builder_cls, mock_render):
+        """Calling main without --render does NOT invoke render_project."""
+        mock_builder = MagicMock()
+        mock_builder_cls.return_value = mock_builder
+
+        with patch("scripts.compose.SampleSelector") as mock_selector:
+            mock_sel_instance = MagicMock()
+            mock_sel_instance.select_one.return_value = None
+            mock_selector.return_value = mock_sel_instance
+
+            with patch("sys.argv", ["compose.py", "--genre", "reggaeton"]):
+                compose_main()
+
+        mock_render.assert_not_called()
+
+    @patch("scripts.compose.render_project")
+    @patch("scripts.compose.RPPBuilder")
+    def test_render_output_overrides_default_wav_path(self, mock_builder_cls, mock_render):
+        """--render-output sets the WAV path explicitly."""
+        mock_builder = MagicMock()
+        mock_builder_cls.return_value = mock_builder
+
+        with patch("scripts.compose.SampleSelector") as mock_selector:
+            mock_sel_instance = MagicMock()
+            mock_sel_instance.select_one.return_value = None
+            mock_selector.return_value = mock_sel_instance
+
+            with patch("sys.argv", [
+                "compose.py",
+                "--genre", "reggaeton",
+                "--render",
+                "--render-output", "output/my_render.wav"
+            ]):
+                compose_main()
+
+        mock_render.assert_called_once()
+        wav_path = mock_render.call_args[0][1]
+        assert wav_path == "output/my_render.wav"
+
+    @patch("scripts.compose.render_project")
+    @patch("scripts.compose.RPPBuilder")
+    def test_render_project_propagates_file_not_found_error(self, mock_builder_cls, mock_render):
+        """FileNotFoundError from render_project is propagated to caller."""
+        mock_builder = MagicMock()
+        mock_builder_cls.return_value = mock_builder
+        mock_render.side_effect = FileNotFoundError("reaper.exe not found")
+
+        with patch("scripts.compose.SampleSelector") as mock_selector:
+            mock_sel_instance = MagicMock()
+            mock_sel_instance.select_one.return_value = None
+            mock_selector.return_value = mock_sel_instance
+
+            with patch("sys.argv", [
+                "compose.py",
+                "--genre", "reggaeton",
+                "--render",
+            ]):
+                with pytest.raises(FileNotFoundError):
+                    compose_main()