fix(markdown_normalizer): adopt safe-by-default strategy for escaping

- Set 'enable_escape_fix' to False by default to prevent accidental corruption
- Improve LaTeX display math identification using regex protection
- Update documentation to reflect opt-in recommendation for escape fixes
- Fix Issue #57 remaining aggressive escaping bugs

tests/plugins/filters/markdown_normalizer/test_issue_57_regression.py

@@ -0,0 +1,22 @@
+from plugins.filters.markdown_normalizer.markdown_normalizer import ContentNormalizer, NormalizerConfig
+
+def test_latex_display_math_protection():
+    """Verify that $$\nabla$$ is NOT broken by escape fix."""
+    config = NormalizerConfig(enable_escape_fix=True)
+    norm = ContentNormalizer(config)
+    
+    # Input has literal backslash + n (represented as \\n in python code)
+    # Total input: $$ \ n a b l a $$
+    text = r"$$\nabla$$"
+    res = norm.normalize(text)
+    
+    # It should NOT change literal \n to a newline inside $$
+    assert "\n" not in res, f"LaTeX display math was corrupted with a real newline: {repr(res)}"
+    assert res == text, f"Expected {repr(text)}, got {repr(res)}"
+
+if __name__ == "__main__":
+    try:
+        test_latex_display_math_protection()
+        print("✅ LaTeX protection test passed.")
+    except AssertionError as e:
+        print(f"❌ LaTeX protection test FAILED: {e}")