Fix: Update HelperConnection.h include paths to use flat includes (Source/Shared is in include dirs)

Fix: Replace MSG_NOSIGNAL (Linux-only) with macOS-compatible send() in HelperConnection.cpp and HelperIPC.cpp

Out-of-process rebuild: Add Plugin/McpServer.cpp — MCP tools route through helper IPC

Out-of-process rebuild: Add Plugin/McpServer.h/.cpp — routes MCP tools through HelperConnection

Out-of-process rebuild: Add Plugin/PluginBridgeEditor.cpp — clean modern dark UI with status indicators

Out-of-process rebuild: Add Plugin/PluginBridgeEditor.h/.cpp — modern minimal dark UI

Out-of-process rebuild: Add Plugin/PluginBridgeProcessor.cpp — routes audio through shared memory to helper

Out-of-process rebuild: Add Plugin/PluginBridgeProcessor.h/.cpp — uses HelperConnection for crash-safe hosting

Out-of-process rebuild: Add Plugin/HelperConnection.cpp — full implementation

Out-of-process rebuild: Add Plugin/HelperConnection.h/.cpp — spawns helper, IPC, crash detection