fix: return 'Unknown' as primary_language when directory has no Python files

app/tools/file_scanner.py

@@ -158,7 +158,7 @@ def scan_repository(local_path: str) -> dict[str, object]:
         except Exception as exc:  # nosec B110
             logger.warning("Failed to count lines", extra={"file": file_path, "error": str(exc)})
 
-    primary_language = max(language_counts, key=lambda k: language_counts[k], default=".py")
+    primary_language = max(language_counts, key=lambda k: language_counts[k], default="")
     lang_name_map = {
         ".py": "Python", ".js": "JavaScript", ".ts": "TypeScript",
         ".go": "Go", ".java": "Java", ".rb": "Ruby", ".rs": "Rust",
@@ -166,7 +166,7 @@ def scan_repository(local_path: str) -> dict[str, object]:
     }
 
     return {
-        "primary_language": lang_name_map.get(primary_language, primary_language),
+        "primary_language": lang_name_map.get(primary_language, primary_language) if primary_language else "Unknown",
         "total_files": total_files,
         "total_lines": total_lines,
         "language_counts": dict(language_counts),