Initial commit: HC900 Crawler

Honeywell HC900을 Modbus TCP로 직접 폴링 → gRPC → C# 크롤러 → PostgreSQL.
기존 Experion OPC UA 데이터 경로를 HC900 직접 통신으로 대체.

- industrial-comm/cpp: C++ Modbus 게이트웨이 (gRPC 서버)
- src: C# .NET 8 ASP.NET Core 크롤러 + 웹 UI (3-Layer)
- mcp-server: Python FastMCP (RAG/NL2SQL/P&ID)
- 다중 컨트롤러(N-Controller) 지원

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

industrial-comm/cpp/include/modbus_tcp.hpp

@@ -0,0 +1,61 @@
+#pragma once
+#include "modbus_exception.hpp"
+#include "itransport.hpp"
+#include "transport_error.hpp"
+
+#include <cstdint>
+#include <vector>
+#include <chrono>
+#include <string>
+
+class ModbusTCP : public ITransport {
+public:
+    ModbusTCP();
+    ~ModbusTCP() override;
+
+    bool connect(const char* host, std::uint16_t port) override;
+    void disconnect() override;
+    bool is_connected() const override;
+  
+    TransportState state() const override { return state_; }
+    TransportError last_error() const override { return last_error_; }
+
+    bool read_registers(std::uint16_t addr,
+                        std::uint16_t count,
+                        std::vector<std::uint16_t>& out) override;    
+
+    bool write_registers(std::uint16_t addr,
+                         const std::vector<std::uint16_t>& values) override;
+
+    void poll() override; // watchdog
+
+    void reset() override;
+
+private:
+    bool reconnect();
+    bool recv_all(void* buf, std::size_t len);
+
+private:
+    // socket
+    int sock_;
+    std::uint16_t transaction_id_{0};
+
+    // connection info
+    std::string host_;
+    std::uint16_t port_{0};
+
+    // state machine
+    TransportState state_{TransportState::Disconnected};
+    TransportError last_error_{TransportError::None};
+    ModbusException exception_;
+
+    // watchdog
+    static constexpr int WATCHDOG_SEC  = 5;
+    static constexpr int MAX_RETRY     = 5;
+    static constexpr int FAULT_RESET_SEC = 30; // Fault 후 자동 리셋 대기
+    std::chrono::steady_clock::time_point last_ok_;
+    std::chrono::steady_clock::time_point fault_since_;
+    int retry_count_{0};
+    bool can_io() const;
+
+};