Add mock Arduino for x86_64 host-side testing

Complete Arduino API mock (mock_arduino.h/cpp) enabling application
code to compile and run on PC without hardware. Includes MockSerial,
String class, GPIO/analog/timing/interrupt mocks with state tracking
and test control API.

- Arduino.h, Wire.h, SPI.h shims intercept includes in test builds
- System test template (test_system.cpp) using SimHal
- CMakeLists.txt builds mock_arduino as static lib, links both suites
- Root test.sh/test.bat with --unit/--system/--clean/--verbose flags
- test.bat auto-detects MSVC via vswhere + vcvarsall.bat
- Doctor reports nuanced compiler status (on PATH vs installed)
- Refresh pulls mock infrastructure into existing projects
- 15 tests passing: 7 unit (MockHal) + 8 system (SimHal)

templates/basic/test/test_system.cpp.tmpl

@@ -0,0 +1,148 @@
+#include <gtest/gtest.h>
+
+#include "mock_arduino.h"
+#include "hal.h"
+#include "sim_hal.h"
+#include "{{PROJECT_NAME}}_app.h"
+
+// ============================================================================
+// System Tests -- exercise full application logic against simulated hardware
+//
+// Unlike unit tests (which verify exact call sequences), system tests
+// run the real application code against SimHal and inspect observable
+// outputs: pin states, serial messages, timing behavior.
+// ============================================================================
+
+class BlinkAppSystemTest : public ::testing::Test {
+protected:
+    void SetUp() override {
+        mock_arduino_reset();
+        sim_.setMillis(0);
+    }
+
+    SimHal sim_;
+};
+
+TEST_F(BlinkAppSystemTest, SetupConfiguresPins) {
+    BlinkApp app(&sim_);
+    app.begin();
+
+    EXPECT_EQ(sim_.getPinMode(13), OUTPUT);
+    EXPECT_EQ(sim_.getPinMode(2), INPUT_PULLUP);
+}
+
+TEST_F(BlinkAppSystemTest, LedTogglesAtCorrectInterval) {
+    BlinkApp app(&sim_);
+    app.begin();
+
+    // LED should be off initially
+    EXPECT_EQ(sim_.getPin(13), LOW);
+
+    // Advance past one slow interval (500ms)
+    sim_.advanceMillis(500);
+    app.update();
+    EXPECT_EQ(sim_.getPin(13), HIGH);
+
+    // Advance another interval
+    sim_.advanceMillis(500);
+    app.update();
+    EXPECT_EQ(sim_.getPin(13), LOW);
+}
+
+TEST_F(BlinkAppSystemTest, LedDoesNotToggleTooEarly) {
+    BlinkApp app(&sim_);
+    app.begin();
+
+    sim_.advanceMillis(499);
+    app.update();
+    EXPECT_EQ(sim_.getPin(13), LOW);
+}
+
+TEST_F(BlinkAppSystemTest, ButtonTogglesFastMode) {
+    BlinkApp app(&sim_, 13, 2);
+    sim_.setPin(2, HIGH);  // Button not pressed (INPUT_PULLUP)
+    app.begin();
+
+    EXPECT_FALSE(app.fastMode());
+
+    // Press button
+    sim_.setPin(2, LOW);
+    app.update();
+    EXPECT_TRUE(app.fastMode());
+    EXPECT_EQ(app.interval(), BlinkApp::FAST_INTERVAL_MS);
+
+    // Release and press again -> back to slow
+    sim_.setPin(2, HIGH);
+    app.update();
+    sim_.setPin(2, LOW);
+    app.update();
+    EXPECT_FALSE(app.fastMode());
+    EXPECT_EQ(app.interval(), BlinkApp::SLOW_INTERVAL_MS);
+}
+
+TEST_F(BlinkAppSystemTest, FastModeBlinksFaster) {
+    BlinkApp app(&sim_, 13, 2);
+    sim_.setPin(2, HIGH);
+    app.begin();
+
+    // Switch to fast mode
+    sim_.setPin(2, LOW);
+    app.update();
+    sim_.setPin(2, HIGH);
+    app.update();
+    EXPECT_TRUE(app.fastMode());
+
+    // Clear log, then count toggles over 1 second
+    sim_.clearGpioLog();
+    for (int i = 0; i < 8; ++i) {
+        sim_.advanceMillis(125);
+        app.update();
+    }
+
+    // In 1 second at 125ms intervals, we expect 8 toggles
+    int high_count = sim_.countWrites(13, HIGH);
+    int low_count = sim_.countWrites(13, LOW);
+    EXPECT_EQ(high_count + low_count, 8);
+}
+
+TEST_F(BlinkAppSystemTest, SerialOutputOnStartup) {
+    BlinkApp app(&sim_);
+    app.begin();
+
+    std::string output = sim_.serialOutput();
+    EXPECT_NE(output.find("BlinkApp started"), std::string::npos);
+}
+
+TEST_F(BlinkAppSystemTest, SerialOutputOnModeChange) {
+    BlinkApp app(&sim_, 13, 2);
+    sim_.setPin(2, HIGH);
+    app.begin();
+    sim_.clearSerialOutput();
+
+    // Press button
+    sim_.setPin(2, LOW);
+    app.update();
+
+    std::string output = sim_.serialOutput();
+    EXPECT_NE(output.find("FAST"), std::string::npos);
+}
+
+// ============================================================================
+// Timing accuracy test -- verifies blink over a longer duration
+// ============================================================================
+
+TEST_F(BlinkAppSystemTest, TenSecondBlinkCount) {
+    BlinkApp app(&sim_);
+    app.begin();
+    sim_.clearGpioLog();
+
+    // Run for 10 seconds at 10ms resolution
+    for (int i = 0; i < 1000; ++i) {
+        sim_.advanceMillis(10);
+        app.update();
+    }
+
+    // At 500ms intervals over 10s, expect 20 toggles
+    int toggles = sim_.countWrites(13, HIGH) + sim_.countWrites(13, LOW);
+    EXPECT_EQ(toggles, 20);
+}