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

.gitattributes

@@ -0,0 +1,29 @@
+# Auto-detect text files and normalize line endings
+* text=auto
+
+# Source code
+*.ino text
+*.cpp text
+*.c text
+*.h text
+*.hpp text
+*.S text
+
+# Scripts
+*.sh text eol=lf
+
+# Config
+*.json text
+*.yaml text
+*.yml text
+*.md text
+*.txt text
+
+# Binary / generated -- do not diff
+*.hex binary
+*.elf binary
+*.bin binary
+*.eep binary
+*.png binary
+*.jpg binary
+*.pdf binary