Phase 1-4: Audio stack, mixer engine, MIDI, and network API

P2-R1: ALSA + JACK2 low-latency config (scripts, quirks, tuning)
P2-R2: Carla integration (build scripts, 8ch rack config, NAM LV2 support)
P2-R3: Plugin manager, categories, blacklist, NAM model support
P3-R1: Mixer DSP engine (channel strip, routing matrix, bus mgr, automation)
P4-R1: MIDI engine (learn mode, clock sync, HID discovery, mapping store)
P4-R2: Network API (OSC server, FastAPI REST, WebSocket, auth, rate limiter)
P5-R1: Touchscreen UI evaluation + main entry point
docs: Audio stack, Carla integration, MIDI support, UI evaluation
tests: Full test suite (292 passing)

main_touch.py

@@ -0,0 +1,85 @@
+#!/usr/bin/env python3
+"""Entry point for the Raspberry Pi Touchscreen Mixer UI.
+
+A Kivy-based multi-touch mixer control surface for the
+Raspberry Pi RT Audio Mixer. Connects to the mixer engine
+via REST API + OSC.
+
+Usage:
+    python3 main_touch.py
+    python3 main_touch.py --host 192.168.1.10 --port 8000
+    python3 main_touch.py --api-key my-secret-key
+    KIVY_DPI=220 python3 main_touch.py
+"""
+
+from __future__ import annotations
+
+import argparse
+import os
+import sys
+
+
+def main():
+    parser = argparse.ArgumentParser(
+        description="Raspberry Pi Touchscreen Mixer UI",
+        formatter_class=argparse.RawDescriptionHelpFormatter,
+        epilog="""
+Examples:
+  %(prog)s                                    # local mixer on :8000
+  %(prog)s --host 192.168.1.10                # remote mixer
+  %(prog)s --host 127.0.0.1 --api-key abc123  # with auth
+  KIVY_DPI=220 %(prog)s                       # force 220 DPI
+
+Environment:
+  MIXER_HOST       mixer hostname (default 127.0.0.1)
+  MIXER_PORT       REST API port (default 8000)
+  MIXER_OSC_PORT   OSC server port (default 9001)
+  MIXER_API_KEY    API key for authentication
+  KIVY_DPI         force screen DPI (auto-detected otherwise)
+        """,
+    )
+    parser.add_argument(
+        "--host", default=os.environ.get("MIXER_HOST", "127.0.0.1"),
+        help="Mixer server hostname (default: 127.0.0.1)",
+    )
+    parser.add_argument(
+        "--port", type=int, default=int(os.environ.get("MIXER_PORT", "8000")),
+        help="REST API port (default: 8000)",
+    )
+    parser.add_argument(
+        "--osc-port", type=int, default=int(os.environ.get("MIXER_OSC_PORT", "9001")),
+        help="OSC server port (default: 9001)",
+    )
+    parser.add_argument(
+        "--api-key", default=os.environ.get("MIXER_API_KEY", ""),
+        help="API key for mixer authentication",
+    )
+
+    args = parser.parse_args()
+
+    # Ensure src is on the path
+    project_root = os.path.dirname(os.path.abspath(__file__))
+    if project_root not in sys.path:
+        sys.path.insert(0, project_root)
+
+    # Import Kivy app (late import after CLI parsing)
+    from src.ui.app import MixerApp
+
+    app = MixerApp(
+        host=args.host,
+        rest_port=args.port,
+        osc_port=args.osc_port,
+        api_key=args.api_key,
+    )
+
+    print(f"Starting touchscreen mixer UI...")
+    print(f"  Mixer server: {args.host}:{args.port}")
+    print(f"  OSC server:   {args.host}:{args.osc_port}")
+    print(f"  Touch to begin. ESC to cycle screens.")
+    print()
+
+    app.run()
+
+
+if __name__ == "__main__":
+    main()