Arduino CLI build system with HAL-based test architecture

Build and upload tool (arduino-build.sh):
- Compile, upload, and monitor via arduino-cli
- Device discovery with USB ID identification (--devices)
- Persistent reconnecting serial monitor (--watch)
- Split compile/upload workflow (--verify, --upload-only)
- First-time setup wizard (--setup)
- Comprehensive --help with troubleshooting and RedBoard specs

Testable application architecture:
- Hardware abstraction layer (lib/hal/) decouples logic from Arduino API
- Google Mock HAL for unit tests (exact call verification)
- Simulated HAL for system tests (GPIO state, virtual clock, I2C devices)
- Example I2C temperature sensor simulator (TMP102)
- Host-side test suite via CMake + Google Test (21 tests)

Example sketch:
- blink/ -- LED blink with button-controlled speed, wired through HAL

lib/hal/hal_arduino.h

@@ -0,0 +1,93 @@
+#ifndef HAL_ARDUINO_H
+#define HAL_ARDUINO_H
+
+/*
+ * Real hardware implementation of the HAL.
+ *
+ * This file includes Arduino.h and Wire.h, so it can only be compiled
+ * by avr-gcc (via arduino-cli). It is included by .ino files only.
+ *
+ * Every method is a trivial passthrough to the real Arduino function.
+ * The point is not to add logic here -- it is to keep Arduino.h out
+ * of your application code so that code can compile on the host.
+ */
+
+#include <Arduino.h>
+#include <Wire.h>
+#include <hal.h>
+
+class ArduinoHal : public Hal {
+public:
+    // -- GPIO ---------------------------------------------------------------
+    void pinMode(uint8_t pin, uint8_t mode) override {
+        ::pinMode(pin, mode);
+    }
+    void digitalWrite(uint8_t pin, uint8_t value) override {
+        ::digitalWrite(pin, value);
+    }
+    uint8_t digitalRead(uint8_t pin) override {
+        return ::digitalRead(pin);
+    }
+    int analogRead(uint8_t pin) override {
+        return ::analogRead(pin);
+    }
+    void analogWrite(uint8_t pin, int value) override {
+        ::analogWrite(pin, value);
+    }
+
+    // -- Timing -------------------------------------------------------------
+    unsigned long millis() override {
+        return ::millis();
+    }
+    unsigned long micros() override {
+        return ::micros();
+    }
+    void delay(unsigned long ms) override {
+        ::delay(ms);
+    }
+    void delayMicroseconds(unsigned long us) override {
+        ::delayMicroseconds(us);
+    }
+
+    // -- Serial -------------------------------------------------------------
+    void serialBegin(unsigned long baud) override {
+        Serial.begin(baud);
+    }
+    void serialPrint(const char* msg) override {
+        Serial.print(msg);
+    }
+    void serialPrintln(const char* msg) override {
+        Serial.println(msg);
+    }
+    int serialAvailable() override {
+        return Serial.available();
+    }
+    int serialRead() override {
+        return Serial.read();
+    }
+
+    // -- I2C ----------------------------------------------------------------
+    void i2cBegin() override {
+        Wire.begin();
+    }
+    void i2cBeginTransmission(uint8_t addr) override {
+        Wire.beginTransmission(addr);
+    }
+    size_t i2cWrite(uint8_t data) override {
+        return Wire.write(data);
+    }
+    uint8_t i2cEndTransmission() override {
+        return Wire.endTransmission();
+    }
+    uint8_t i2cRequestFrom(uint8_t addr, uint8_t count) override {
+        return Wire.requestFrom(addr, count);
+    }
+    int i2cAvailable() override {
+        return Wire.available();
+    }
+    int i2cRead() override {
+        return Wire.read();
+    }
+};
+
+#endif // HAL_ARDUINO_H