fix: add configurable kebab-case filename format to resolve forward slash inconsistency

- Add filename_format config option with "kebab-case" as default
- Create sanitize_filename() utility to convert titles to safe filenames
- Modify Entity.file_path to use sanitized filenames when configured
- Add comprehensive tests for new functionality
- Resolves inconsistency between file paths and permalinks for titles with forward slashes

Fixes #154

Co-authored-by: Drew Cain <groksrc@users.noreply.github.com>

tests/utils/test_permalink_formatting.py

@@ -7,7 +7,7 @@ import pytest
 from basic_memory.config import ProjectConfig
 from basic_memory.services import EntityService
 from basic_memory.sync.sync_service import SyncService
-from basic_memory.utils import generate_permalink
+from basic_memory.utils import generate_permalink, sanitize_filename
 
 
 async def create_test_file(path: Path, content: str = "test content") -> None:
@@ -118,3 +118,92 @@ def test_chinese_character_preservation(input_path, expected):
 def test_mixed_character_sets(input_path, expected):
     """Test handling of mixed character sets and edge cases."""
     assert generate_permalink(input_path) == expected
+
+
+@pytest.mark.parametrize(
+    "input_title, expected",
+    [
+        ("Coupon Enable/Disable Feature", "coupon-enable-disable-feature"),
+        ("My Awesome Feature", "my-awesome-feature"),
+        ("Test_File Name.txt", "test-file-name-txt"),
+        ("Feature/With/Multiple/Slashes", "feature-with-multiple-slashes"),
+        ("Mixed Case Feature", "mixed-case-feature"),
+        ("  Leading and trailing spaces  ", "leading-and-trailing-spaces"),
+        ("Special!@#$%^&*()Characters", "special-characters"),
+        ("北京/东京", "北京-东京"),
+        ("Mixed/中文/English", "mixed-中文-english"),
+    ],
+)
+def test_sanitize_filename(input_title, expected):
+    """Test that title sanitization works correctly for filenames."""
+    assert sanitize_filename(input_title) == expected
+
+
+@pytest.mark.asyncio
+async def test_entity_file_path_with_kebab_case_config(
+    sync_service: SyncService, project_config: ProjectConfig, entity_service: EntityService
+):
+    """Test that Entity file_path uses kebab-case when configured."""
+    # Test with kebab-case enabled (default)
+    from basic_memory.schemas.base import Entity
+    from basic_memory.config import app_config
+    
+    # Ensure config is set to kebab-case 
+    original_format = app_config.filename_format
+    app_config.filename_format = "kebab-case"
+    
+    try:
+        entity = Entity(
+            title="Coupon Enable/Disable Feature",
+            folder="bugs",
+            content="Test content"
+        )
+        
+        # With kebab-case, forward slashes should be converted to hyphens
+        expected_file_path = "bugs/coupon-enable-disable-feature.md"
+        expected_permalink = "bugs/coupon-enable-disable-feature"
+        
+        assert entity.file_path == expected_file_path
+        assert entity.permalink == expected_permalink
+        
+        # Test that file_path and permalink are now consistent
+        assert entity.permalink == generate_permalink(entity.file_path)
+        
+    finally:
+        # Restore original configuration
+        app_config.filename_format = original_format
+
+
+@pytest.mark.asyncio
+async def test_entity_file_path_with_original_config(
+    sync_service: SyncService, project_config: ProjectConfig, entity_service: EntityService
+):
+    """Test that Entity file_path preserves original format when configured."""
+    from basic_memory.schemas.base import Entity
+    from basic_memory.config import app_config
+    
+    # Set config to original format
+    original_format = app_config.filename_format
+    app_config.filename_format = "original"
+    
+    try:
+        entity = Entity(
+            title="Coupon Enable/Disable Feature",
+            folder="bugs",
+            content="Test content"
+        )
+        
+        # With original format, spaces and slashes are preserved
+        # This creates the inconsistency that the issue reports
+        expected_file_path = "bugs/Coupon Enable/Disable Feature.md"
+        expected_permalink = "bugs/coupon-enable-disable-feature"
+        
+        assert entity.file_path == expected_file_path
+        assert entity.permalink == expected_permalink
+        
+        # This demonstrates the inconsistency when using original format
+        assert entity.permalink != generate_permalink(entity.file_path)
+        
+    finally:
+        # Restore original configuration
+        app_config.filename_format = original_format