Add Python REPL widget for WebGL build

Features:
- JSFiddle-style code editor panel alongside game canvas
- Run button (or Ctrl+Enter) executes Python code
- Reset button reloads game.py
- Tab key inserts 4 spaces for proper indentation
- Shows >>> prompt with code preview
- Displays repr of last expression (like Python REPL)
- Error highlighting in red, success in green
- Canvas focus handling with visual indicator

C++ exports (callable from JavaScript):
- run_python_string(code) - simple execution
- run_python_string_with_output(code) - captures stdout/stderr + expr repr
- reset_python_environment() - reloads game.py

JavaScript API available in console:
- runPython(code) - execute Python and get output
- resetGame() - reset to initial state
- FS.readFile/writeFile - access virtual filesystem

Also fixes canvas focus issues on page load.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/platform/EmscriptenStubs.cpp

@@ -7,6 +7,9 @@
 #include <sys/resource.h>
 #include <wchar.h>
 #include <errno.h>
+#include <emscripten.h>
+#include <Python.h>
+#include <string>
 
 extern "C" {
 
@@ -33,6 +36,134 @@ size_t wcsftime(wchar_t *wcs, size_t maxsize, const wchar_t *format, const struc
     return 0;
 }
 
+// =============================================================================
+// JavaScript-callable Python execution functions
+// =============================================================================
+
+// Run a Python string and return the result code (0 = success, -1 = error)
+EMSCRIPTEN_KEEPALIVE
+int run_python_string(const char* code) {
+    if (!Py_IsInitialized()) {
+        return -1;
+    }
+    return PyRun_SimpleString(code);
+}
+
+// Run Python code and capture stdout/stderr as a string
+// Returns a pointer to a static buffer (caller should copy immediately)
+static std::string python_output_buffer;
+
+EMSCRIPTEN_KEEPALIVE
+const char* run_python_string_with_output(const char* code) {
+    if (!Py_IsInitialized()) {
+        python_output_buffer = "Error: Python not initialized";
+        return python_output_buffer.c_str();
+    }
+
+    // Redirect stdout and stderr to a StringIO, run code, capture output
+    // Also capture repr of last expression (like Python REPL)
+    const char* capture_code = R"(
+import sys
+import io
+
+_mcrf_stdout_capture = io.StringIO()
+_mcrf_stderr_capture = io.StringIO()
+_mcrf_old_stdout = sys.stdout
+_mcrf_old_stderr = sys.stderr
+sys.stdout = _mcrf_stdout_capture
+sys.stderr = _mcrf_stderr_capture
+
+_mcrf_exec_error = None
+_mcrf_last_repr = None
+
+try:
+    # Try to compile as eval (expression) first
+    _mcrf_code_obj = compile(_mcrf_user_code, '<repl>', 'eval')
+    _mcrf_result = eval(_mcrf_code_obj, globals())
+    if _mcrf_result is not None:
+        _mcrf_last_repr = repr(_mcrf_result)
+except SyntaxError:
+    # Not a simple expression, try exec
+    try:
+        exec(_mcrf_user_code, globals())
+    except Exception as e:
+        import traceback
+        _mcrf_exec_error = traceback.format_exc()
+except Exception as e:
+    import traceback
+    _mcrf_exec_error = traceback.format_exc()
+
+sys.stdout = _mcrf_old_stdout
+sys.stderr = _mcrf_old_stderr
+
+_mcrf_captured_output = _mcrf_stdout_capture.getvalue()
+if _mcrf_stderr_capture.getvalue():
+    _mcrf_captured_output += _mcrf_stderr_capture.getvalue()
+if _mcrf_exec_error:
+    _mcrf_captured_output += _mcrf_exec_error
+elif _mcrf_last_repr:
+    _mcrf_captured_output += _mcrf_last_repr
+)";
+
+    // Set the user code as a Python variable
+    PyObject* main_module = PyImport_AddModule("__main__");
+    PyObject* main_dict = PyModule_GetDict(main_module);
+    PyObject* py_code = PyUnicode_FromString(code);
+    PyDict_SetItemString(main_dict, "_mcrf_user_code", py_code);
+    Py_DECREF(py_code);
+
+    // Run the capture code
+    PyRun_SimpleString(capture_code);
+
+    // Get the captured output
+    PyObject* output = PyDict_GetItemString(main_dict, "_mcrf_captured_output");
+    if (output && PyUnicode_Check(output)) {
+        const char* output_str = PyUnicode_AsUTF8(output);
+        python_output_buffer = output_str ? output_str : "";
+    } else {
+        python_output_buffer = "";
+    }
+
+    // Clean up temporary variables
+    PyDict_DelItemString(main_dict, "_mcrf_user_code");
+    PyDict_DelItemString(main_dict, "_mcrf_stdout_capture");
+    PyDict_DelItemString(main_dict, "_mcrf_stderr_capture");
+    PyDict_DelItemString(main_dict, "_mcrf_old_stdout");
+    PyDict_DelItemString(main_dict, "_mcrf_old_stderr");
+    PyDict_DelItemString(main_dict, "_mcrf_exec_error");
+    PyDict_DelItemString(main_dict, "_mcrf_captured_output");
+
+    return python_output_buffer.c_str();
+}
+
+// Reset the Python environment (re-run game.py)
+EMSCRIPTEN_KEEPALIVE
+int reset_python_environment() {
+    if (!Py_IsInitialized()) {
+        return -1;
+    }
+
+    // Clear all scenes and reload game.py
+    const char* reset_code = R"(
+import mcrfpy
+import sys
+
+# Try to reload the game module
+if 'game' in sys.modules:
+    del sys.modules['game']
+
+# Re-execute game.py
+try:
+    with open('/scripts/game.py', 'r') as f:
+        exec(f.read(), globals())
+    print("Environment reset successfully")
+except Exception as e:
+    print(f"Reset error: {e}")
+)";
+
+    return PyRun_SimpleString(reset_code);
+}
+
 } // extern "C"
 
 #endif // __EMSCRIPTEN__