fix: guard against None stdout in fix_console_encoding for pythonw.exe

When launched via pythonw.exe (no console), sys.stdout/stderr are None.
Accessing .encoding on None raised AttributeError, caught by the GUI's
pipeline import guard and shown as 'Failed to load pipeline'. Added
None check before the encoding check in fix_console_encoding(), added
a test, and documented the pitfall in CLAUDE.md.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

test_suite.py

@@ -2076,8 +2076,21 @@ test("compat: _read_os_release parses key=value pairs",                  _test_r
 test("compat: _read_os_release returns {} when file missing",            _test_read_os_release_handles_missing_file)
 test("compat: _is_headless returns False when DISPLAY is set",           _test_is_headless_with_display)
 test("compat: _is_headless returns True when no display env vars",       _test_is_headless_without_display)
+def _test_fix_console_encoding_none_stdout():
+    """fix_console_encoding is a no-op when sys.stdout is None (pythonw.exe)."""
+    original_stdout = sys.stdout
+    try:
+        with _patch("arma_modlist_tools.compat.is_windows", return_value=True):
+            sys.stdout = None
+            _compat_mod.fix_console_encoding()  # must not raise
+            assert sys.stdout is None
+    finally:
+        sys.stdout = original_stdout
+
+
 test("compat: fix_console_encoding is no-op on non-Windows",             _test_fix_console_encoding_non_windows_noop)
 test("compat: fix_console_encoding skips when stdout already UTF-8",     _test_fix_console_encoding_already_utf8)
+test("compat: fix_console_encoding is no-op when stdout is None",        _test_fix_console_encoding_none_stdout)
 
 
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