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

test/run_tests.sh

@@ -0,0 +1,84 @@
+#!/usr/bin/env bash
+#
+# run_tests.sh -- Build and run host-side unit and system tests
+#
+# Usage:
+#   ./test/run_tests.sh              Build and run all tests
+#   ./test/run_tests.sh --clean      Clean rebuild
+#   ./test/run_tests.sh --verbose    Verbose test output
+#   ./test/run_tests.sh --filter X   Run only tests matching X
+#
+# Prerequisites:
+#   cmake >= 3.14, g++ or clang++, git (for fetching gtest)
+#
+# First run will download Google Test (~30 seconds).
+
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+BUILD_DIR="$SCRIPT_DIR/build"
+
+# Color output
+if [[ -t 1 ]]; then
+    RED=$'\033[0;31m'; GRN=$'\033[0;32m'; CYN=$'\033[0;36m'
+    BLD=$'\033[1m';    RST=$'\033[0m'
+else
+    RED=''; GRN=''; CYN=''; BLD=''; RST=''
+fi
+
+info() { echo -e "${CYN}[TEST]${RST}  $*"; }
+ok()   { echo -e "${GRN}[PASS]${RST}  $*"; }
+die()  { echo -e "${RED}[FAIL]${RST}  $*" >&2; exit 1; }
+
+# Parse args
+DO_CLEAN=0
+VERBOSE=""
+FILTER=""
+
+for arg in "$@"; do
+    case "$arg" in
+        --clean)    DO_CLEAN=1 ;;
+        --verbose)  VERBOSE="--verbose" ;;
+        --filter)   : ;;  # next arg is the pattern
+        -*)         die "Unknown option: $arg" ;;
+        *)          FILTER="$arg" ;;
+    esac
+done
+
+# Check prerequisites
+command -v cmake &>/dev/null || die "cmake not found. Install: sudo apt install cmake"
+command -v g++ &>/dev/null || command -v clang++ &>/dev/null || die "No C++ compiler found"
+command -v git &>/dev/null || die "git not found (needed to fetch Google Test)"
+
+# Clean if requested
+if [[ $DO_CLEAN -eq 1 ]] && [[ -d "$BUILD_DIR" ]]; then
+    info "Cleaning build directory..."
+    rm -rf "$BUILD_DIR"
+fi
+
+# Configure
+if [[ ! -f "$BUILD_DIR/CMakeCache.txt" ]]; then
+    info "Configuring (first run will fetch Google Test)..."
+    cmake -S "$SCRIPT_DIR" -B "$BUILD_DIR" -DCMAKE_BUILD_TYPE=Debug
+fi
+
+# Build
+info "Building tests..."
+cmake --build "$BUILD_DIR" --parallel
+
+# Run
+echo ""
+info "${BLD}Running tests...${RST}"
+echo ""
+
+CTEST_ARGS=("--test-dir" "$BUILD_DIR" "--output-on-failure")
+[[ -n "$VERBOSE" ]] && CTEST_ARGS+=("--verbose")
+[[ -n "$FILTER" ]]  && CTEST_ARGS+=("-R" "$FILTER")
+
+if ctest "${CTEST_ARGS[@]}"; then
+    echo ""
+    ok "${BLD}All tests passed.${RST}"
+else
+    echo ""
+    die "Some tests failed."
+fi