fix: keep tests and doc generators away from the developer's config files

test_docsphinx pointed EOS_DIR/EOS_CONFIG_DIR at an empty temporary
directory. EOS then fell back to the config file in the user config
directory, migrated it and wrote it back with a timestamped backup. The
test now writes an empty config file into the temporary directory, as
server_base does.

Additional fixes
- Decode the Sphinx output in test_sphinx_build as UTF-8; on Windows the
  default code page failed and the test reported a NoneType error.
- Check the user config directory with the app author in
  --check-config-side-effect, as EOS does; on Windows the check looked at
  the wrong directory.
- Let the doc generators create EOS' config file in a temporary directory.
  They left an EOS.config.json in the working directory, and a following
  make test-ci then failed in every test.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/generate_config_md.py

@@ -6,6 +6,7 @@ import json
 import os
 import re
 import sys
+import tempfile
 import textwrap
 from pathlib import Path
 from typing import Any, Optional, Type, TypeVar, Union, get_args
@@ -524,4 +525,9 @@ def main():
         ConfigEOS._force_documentation_mode = False
 
 if __name__ == "__main__":
-    main()
+    # EOS creates a config file if it finds none. Let it do so in a temporary
+    # directory, not in the working directory (e.g. the repository root).
+    with tempfile.TemporaryDirectory(prefix="eos-docs-") as eos_dir:
+        os.environ["EOS_DIR"] = eos_dir
+        os.environ["EOS_CONFIG_DIR"] = eos_dir
+        main()