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.py

@@ -0,0 +1,105 @@
+"""Tests for src/reaper_builder/render.py — render_project."""
+
+import sys
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).parents[1]))
+
+import pytest
+from unittest.mock import patch, MagicMock
+from src.reaper_builder.render import render_project
+
+
+class TestRenderProjectFileNotFound:
+    """Test render_project raises FileNotFoundError when reaper.exe path doesn't exist."""
+
+    def test_render_project_raises_file_not_found_for_nonexistent_reaper_exe(self):
+        """FileNotFoundError is raised when reaper.exe does not exist."""
+        nonexistent = Path("C:/Program Files/NONEXISTENT_REAPER/reaper.exe")
+        if nonexistent.exists():
+            pytest.skip("Nonexistent path actually exists — cannot test this")
+
+        with pytest.raises(FileNotFoundError):
+            render_project(
+                rpp_path="input.rpp",
+                output_wav="output.wav",
+                reaper_exe=nonexistent,
+            )
+
+    def test_render_project_raises_file_not_found_default_path(self):
+        """FileNotFoundError raised when default reaper.exe doesn't exist and none provided."""
+        # Patch DEFAULT_REAPER_EXE to a definitely-nonexistent path
+        with patch("src.reaper_builder.render.DEFAULT_REAPER_EXE", Path("/no/such/reaper.exe")):
+            with pytest.raises(FileNotFoundError):
+                render_project(
+                    rpp_path="input.rpp",
+                    output_wav="output.wav",
+                    reaper_exe=None,
+                )
+
+
+class TestRenderProjectSubprocessError:
+    """Test render_project raises RuntimeError when subprocess returns non-zero exit code."""
+
+    def test_render_project_raises_runtime_error_on_nonzero_exit(self):
+        """RuntimeError is raised when subprocess.run returns non-zero returncode."""
+        from src.reaper_builder.render import DEFAULT_REAPER_EXE
+
+        # Check if reaper exists — if not, skip
+        if not DEFAULT_REAPER_EXE.exists():
+            pytest.skip(f"REAPER not installed at {DEFAULT_REAPER_EXE}")
+
+        # Create a minimal valid .rpp for this test
+        import tempfile
+        with tempfile.NamedTemporaryFile(mode="w", suffix=".rpp", delete=False, encoding="utf-8") as f:
+            rpp_path = f.name
+            f.write('<REAPER_PROJECT 0.1 "6.0" 0\n>\n')
+
+        with tempfile.NamedTemporaryFile(suffix=".wav", delete=False) as f:
+            wav_path = f.name
+
+        try:
+            # Mock subprocess.run to return non-zero
+            mock_result = MagicMock()
+            mock_result.returncode = 1
+            mock_result.stdout = ""
+            mock_result.stderr = "Test error"
+
+            with patch("subprocess.run", return_value=mock_result):
+                with pytest.raises(RuntimeError) as exc_info:
+                    render_project(rpp_path=rpp_path, output_wav=wav_path)
+                assert "1" in str(exc_info.value) or "failed" in str(exc_info.value).lower()
+        finally:
+            Path(rpp_path).unlink(missing_ok=True)
+            Path(wav_path).unlink(missing_ok=True)
+
+    def test_render_project_raises_runtime_error_with_error_message(self):
+        """RuntimeError output includes stdout/stderr from REAPER failure."""
+        from src.reaper_builder.render import DEFAULT_REAPER_EXE
+
+        if not DEFAULT_REAPER_EXE.exists():
+            pytest.skip(f"REAPER not installed at {DEFAULT_REAPER_EXE}")
+
+        import tempfile
+        with tempfile.NamedTemporaryFile(mode="w", suffix=".rpp", delete=False, encoding="utf-8") as f:
+            rpp_path = f.name
+            f.write('<REAPER_PROJECT 0.1 "6.0" 0\n>\n')
+
+        with tempfile.NamedTemporaryFile(suffix=".wav", delete=False) as f:
+            wav_path = f.name
+
+        try:
+            mock_result = MagicMock()
+            mock_result.returncode = 2
+            mock_result.stdout = "standard output text"
+            mock_result.stderr = "error output text"
+
+            with patch("subprocess.run", return_value=mock_result):
+                with pytest.raises(RuntimeError) as exc_info:
+                    render_project(rpp_path=rpp_path, output_wav=wav_path)
+                # Error message should include the exit code or stderr
+                err_str = str(exc_info.value)
+                assert "2" in err_str or "error output text" in err_str
+        finally:
+            Path(rpp_path).unlink(missing_ok=True)
+            Path(wav_path).unlink(missing_ok=True)