feat: Add Windows compatibility support

Add cross-platform utilities and guidelines to ensure the Empathy Framework
works correctly on Windows, macOS, and Linux.

Changes:
- Add platform_utils.py module with:
  - Platform detection (is_windows, is_macos, is_linux)
  - Platform-appropriate directories (logs, data, config, cache)
  - Asyncio Windows event loop policy handling
  - UTF-8 file utilities
  - Path normalization helpers

- Fix hardcoded Unix paths:
  - audit_logger.py: Use platform-appropriate default log directory
  - cli.py: Call setup_asyncio_policy() at startup

- Add cross-platform coding guidelines to python-standards.md:
  - File path handling with pathlib
  - UTF-8 encoding for text files
  - Asyncio policy setup for Windows
  - Testing guidance for multi-platform

- Add check_platform_compat.py script for CI integration:
  - Detects hardcoded paths, missing encoding, asyncio issues
  - JSON output for CI parsing
  - --strict mode for blocking builds

- Add comprehensive tests (40 tests in test_platform_utils.py)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: 2 people

.claude/python-standards.md

@@ -4,3 +4,80 @@
 - Follow PEP 8
 - Write docstrings
 - Target 90%+ test coverage
+
+## Cross-Platform Compatibility
+
+The Empathy Framework must work on Windows, macOS, and Linux. Follow these guidelines:
+
+### File Paths
+
+- **Always use `pathlib.Path`** instead of string concatenation for paths
+- **Never hardcode path separators** (`/` or `\`)
+- **Use `empathy_os.platform_utils`** for OS-specific directories:
+
+  ```python
+  from empathy_os.platform_utils import get_default_log_dir, get_default_data_dir
+
+  # Good: Platform-appropriate paths
+  log_dir = get_default_log_dir()  # ~/Library/Logs/empathy on macOS, %APPDATA%/empathy/logs on Windows
+
+  # Bad: Hardcoded Unix path
+  log_dir = Path("/var/log/empathy")
+  ```
+
+### File Encoding
+
+- **Always specify `encoding="utf-8"`** when opening text files:
+
+  ```python
+  # Good
+  with open(path, "r", encoding="utf-8") as f:
+      content = f.read()
+
+  # Bad (Windows defaults to cp1252)
+  with open(path, "r") as f:
+      content = f.read()
+  ```
+
+- Use `empathy_os.platform_utils.read_text_file()` and `write_text_file()` for convenience
+
+### Asyncio
+
+- **Call `setup_asyncio_policy()`** before any `asyncio.run()` in CLI entry points:
+
+  ```python
+  from empathy_os.platform_utils import setup_asyncio_policy
+
+  def main():
+      setup_asyncio_policy()  # Required for Windows compatibility
+      asyncio.run(async_main())
+  ```
+
+- Windows requires `WindowsSelectorEventLoopPolicy` for compatibility with many libraries
+
+### Line Endings
+
+- Git handles line endings via `.gitattributes`
+- When writing files programmatically, use `\n` (Git will convert on checkout)
+
+### Environment Variables
+
+- Use `os.environ.get()` with sensible defaults
+- Remember Windows uses different variable names (`%APPDATA%` vs `$HOME`)
+
+### Subprocess Calls
+
+- Use `subprocess.run()` with `shell=False` when possible
+- Avoid shell-specific syntax (pipes, redirects) in subprocess calls
+- Use `shlex.split()` on Unix, but note it doesn't work on Windows
+
+### Testing
+
+- Mock `platform.system()` to test all OS paths:
+
+  ```python
+  with patch("platform.system", return_value="Windows"):
+      assert is_windows() is True
+  ```
+
+- Run tests on all platforms via CI (see `.github/workflows/tests.yml` - runs on ubuntu, macos, windows)