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

blink/blink.ino

@@ -0,0 +1,32 @@
+/*
+ * blink.ino -- LED blink with button-controlled speed
+ *
+ * This .ino file is just the entry point. All logic lives in
+ * BlinkApp (lib/app/blink_app.h) which depends on the HAL
+ * interface (lib/hal/hal.h), making it testable on the host.
+ *
+ * The build script auto-discovers lib/ subdirectories and passes
+ * them as --library flags to arduino-cli, so angle-bracket includes
+ * work for project-local libraries.
+ *
+ * Wiring:
+ *   Pin 13 (LED_BUILTIN) -- onboard LED (no wiring needed)
+ *   Pin 2                -- momentary button to GND (uses INPUT_PULLUP)
+ *
+ * Serial: 115200 baud
+ *   Prints "FAST" or "SLOW" on button press.
+ */
+
+#include <hal_arduino.h>
+#include <blink_app.h>
+
+static ArduinoHal hw;
+static BlinkApp app(&hw);
+
+void setup() {
+    app.begin();
+}
+
+void loop() {
+    app.update();
+}