bridge: fix Qin VST2 silent playback via per-child SHM sandbox

- out-of-process VST2 sandbox: each Qin track spawns its own plugin_host.exe child
  with unique SHM (SonicForge_PluginHost2_<bridgePid>_<ch>_<seq>), watchdog <=3 respawns
- preset round-trip bridge<->child over SHM (presetIn/presetOut 64KB), stub rejection MIN_PRESET=100
- seed qin_default.b64 default preset into every fresh child; saved patch wins on restore
- forward MIDI on channel 0 (Qin_RV only listens on ch0); one instrument per child
- controls 4/5/6 = OPEN_GUI/CLOSE_GUI/QUIT
- gitignore runtime carla_projects

native_bridge/include/SharedMemoryIPC.h

@@ -87,11 +87,22 @@ struct SharedAudioBufferIPC {
 // The child renders into the slot it is NOT publishing (writeSlot flips),
 // then publishes; the bridge reads the published slot. A stale slot is safe
 // to read (bridge keeps last block), so a slow child never tears audio.
+// G4.5: preset blob round-trip for VST2 sandbox children. jBridge romplers
+// like Kong Audio Qin_RV render SILENT from factory state - they need their
+// program/bank chunk restored (bridge_state presetBase64). presetIn is
+// bridge->child (base64 text; presetInLen>0 = pending, child applies and
+// zeroes it). presetOut is child->bridge: the child republishes its chunk
+// after load / preset apply / GUI edit, so the bridge can persist it.
+#define PRESET_BLOB_SIZE 65536
 struct SandboxHostIPC {
     SharedAudioBufferIPC base;            // MIDI/control/heartbeat, offsets unchanged
     volatile uint32_t writeSlot;          // 0 or 1: slot the child finished writing
     float audioLeft[2][AUDIO_BLOCK_SIZE]; // 2 full blocks
     float audioRight[2][AUDIO_BLOCK_SIZE];
+    char presetIn[PRESET_BLOB_SIZE];      // bridge -> child (base64 text)
+    volatile uint32_t presetInLen;        // >0: pending; child applies + zeroes
+    char presetOut[PRESET_BLOB_SIZE];     // child -> bridge (base64 text)
+    volatile uint32_t presetOutLen;       // 0 = none published yet
 };
 
 // Shared-memory helpers (impl in SharedMemoryIPC.cpp).