refactor: implement Default trait for new() methods

Add Default trait implementations for SourceFileExtractor and FileStorage
to follow Rust conventions and suppress clippy warnings.

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

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

Author: unhappychoice

src/domain/services/source_file_extractor/source_file_extractor.rs

@@ -9,6 +9,12 @@ pub struct SourceFileExtractor {
     file_storage: FileStorage,
 }
 
+impl Default for SourceFileExtractor {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 impl SourceFileExtractor {
     pub fn new() -> Self {
         Self {
@@ -93,7 +99,7 @@ impl SourceFileExtractor {
         Ok(files)
     }
 
-    fn is_supported_language(&self, path: &PathBuf) -> bool {
+    fn is_supported_language(&self, path: &Path) -> bool {
         path.extension()
             .and_then(|e| e.to_str())
             .map(|extension| Languages::from_extension(extension).is_some())

src/infrastructure/storage/file_storage.rs

@@ -121,6 +121,12 @@ mod mock_impl {
 
     impl AppDataProvider for FileStorage {}
 
+    impl Default for FileStorage {
+        fn default() -> Self {
+            Self::new()
+        }
+    }
+
     impl FileStorage {
         pub fn new() -> Self {
             Self { files: Vec::new() }