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

.gitignore

@@ -0,0 +1,28 @@
+# Build artifacts (arduino-cli output)
+/tmp/arduino-build/
+*.elf
+*.hex
+*.bin
+*.map
+*.eep
+
+# Compiled object files
+*.o
+*.d
+
+# Arduino IDE (if someone opens it there)
+build/
+*.ino.cpp
+
+# Editor files
+.vscode/c_cpp_properties.json
+.vscode/ipch/
+*.swp
+*.swo
+*~
+.idea/
+*.sublime-workspace
+
+# OS junk
+.DS_Store
+Thumbs.db