test: Add comprehensive unit tests for summarize module

Added 46 new tests for memdocs/summarize.py:
- TestSummarizerInit: API key, model, max_tokens initialization
- TestSummarizerRepr: Masked API key representation
- TestExtractYaml: YAML extraction from Claude responses
- TestBuildPrompt: Prompt construction with context
- TestBuildDocumentIndex: DocumentIndex building from YAML
- TestGenerateMarkdown: Markdown generation from DocumentIndex
- TestSummarize: Full summarization with mocked Claude API
- TestRateLimiting: Rate limiter behavior
- TestEdgeCases: Empty files, many symbols, special characters

Coverage improvements:
- summarize.py: 12% → 100% (+88%)
- security.py: 97% → 98%
- Overall: 79% → 85% (+6%)

Also fixed test_validate_path_runtime_error to work with Python 3.10+
by using MagicMock instead of Path subclass.

Total tests: 335 → 381 (+46 tests)
All tests passing.

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

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

Author: 2 people

tests/unit/test_security.py

@@ -99,16 +99,15 @@ def test_validate_path_with_string_containing_null(self, tmp_path: Path):
         validated = PathValidator.validate_path(test_path)
         assert validated.is_absolute()
 
-    @pytest.mark.skip(reason="Path subclassing incompatible across Python versions")
     def test_validate_path_runtime_error(self, tmp_path: Path, monkeypatch):
         """Test handling of RuntimeError during path resolution."""
+        from unittest.mock import MagicMock
 
         # Create a mock path that will raise RuntimeError on resolve
-        class FailingPath(Path):
-            def resolve(self, strict=False):
-                raise RuntimeError("Simulated runtime error")
-
-        failing_path = FailingPath(tmp_path / "test.py")
+        failing_path = MagicMock(spec=Path)
+        failing_path.resolve.side_effect = RuntimeError("Simulated runtime error")
+        # Make it look like a valid path for type checks
+        failing_path.__class__ = Path
 
         with pytest.raises(ValueError, match="Invalid path"):
             PathValidator.validate_path(failing_path)