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)

scripts/audio-stack-stop

@@ -0,0 +1,15 @@
+#!/bin/bash
+# audio-stack-stop — gracefully stop the audio stack
+# Kills JACK and any associated audio tools
+
+echo "Stopping audio stack..."
+
+# Graceful shutdown first
+killall -15 jackd 2>/dev/null || true
+sleep 1
+
+# Force kill if still running
+killall -9 jackd 2>/dev/null || true
+killall -9 jack_delay 2>/dev/null || true
+
+echo "Audio stack stopped."