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/mocks/Wire.h

@@ -0,0 +1,35 @@
+/*
+ * Wire.h -- shim for host-side test builds.
+ *
+ * Intercepts #include <Wire.h> so that code referencing Wire compiles
+ * on x86_64. The mock Arduino state handles I2C through the HAL layer,
+ * but if student code or libraries reference Wire directly, this
+ * prevents a compile error.
+ *
+ * Generated by Anvil.
+ */
+#ifndef WIRE_H_MOCK_SHIM
+#define WIRE_H_MOCK_SHIM
+
+#include "mock_arduino.h"
+
+class MockWire {
+public:
+    void begin() {}
+    void begin(uint8_t) {}
+    void beginTransmission(uint8_t) {}
+    uint8_t endTransmission(bool sendStop = true) { (void)sendStop; return 0; }
+    uint8_t requestFrom(uint8_t addr, uint8_t count, bool sendStop = true) {
+        (void)addr; (void)count; (void)sendStop;
+        return 0;
+    }
+    size_t write(uint8_t data) { (void)data; return 1; }
+    size_t write(const uint8_t* data, size_t len) { (void)data; return len; }
+    int available() { return 0; }
+    int read() { return -1; }
+    void setClock(uint32_t freq) { (void)freq; }
+};
+
+extern MockWire Wire;
+
+#endif // WIRE_H_MOCK_SHIM