feat: native host bridge integration — C++ bridge, Rust SHM, JS routing, build scripts, docs

- native_bridge/: InstrumentEngineManager multi-channel, sample-accurate, CC/program/pitchbend, transport, Vst3Instrument stub (HAVE_VST3SDK)
- src-tauri: shm.rs, bridge spawn + audio pump + health monitor, open_vst_gui, externalBin, commands
- app: UnifiedMidiRouter, NativeBridgeService, bridgeAudioNode, audioRoutingEngine, Plugin Manager UI, Bridge/WASM indicator, set_position sync
- build: 3 ps1 (force-added, build/ ignored), verify_bundle --check-bridge, CI workflow
- docs: TASKS.md, TEST_NOTES.md (Windows verify checklist), install/report updates

app/static/js/services/audioRoutingEngine.js

@@ -0,0 +1,40 @@
+// app/static/js/services/audioRoutingEngine.js
+// Routes the native bridge audio node into the DAW graph:
+//   bridge node -> track.sfEntry (FX rack chain) -> fader/pan -> masterBus
+// Falls back to masterBus.input when no per-track sfEntry exists.
+(function () {
+  var engine = {
+    _connected: false,
+    _trackId: null,
+
+    isConnected: function () { return this._connected; },
+
+    /** bridgeNode = window.BridgeAudioNode; trackCtx = track node ({ sfEntry, gainNode }). */
+    connect: function (bridgeNode, trackCtx, trackId) {
+      if (!bridgeNode || !bridgeNode.getOutputNode) return false;
+      this.disconnect();
+      var dest = null;
+      if (trackCtx && trackCtx.sfEntry) dest = trackCtx.sfEntry;
+      else if (trackCtx && trackCtx.gainNode) dest = trackCtx.gainNode;
+      else if (window.masterBus && window.masterBus.input) dest = window.masterBus.input;
+      if (!dest) {
+        console.warn('[AudioRoutingEngine] no destination (no trackCtx / masterBus)');
+        return false;
+      }
+      if (!bridgeNode.isReady()) bridgeNode.init();
+      bridgeNode.connect(dest);
+      this._connected = true;
+      this._trackId = trackId || null;
+      console.log('[AudioRoutingEngine] bridge audio -> ' + (trackId || 'masterBus'));
+      return true;
+    },
+
+    disconnect: function () {
+      if (window.BridgeAudioNode) window.BridgeAudioNode.disconnect();
+      this._connected = false;
+      this._trackId = null;
+    }
+  };
+
+  window.AudioRoutingEngine = engine;
+})();