fix: resolve lint and typecheck errors in validator.py

Remove unused `import jsonschema` (F401) and add explicit type
annotation for json.load() return value to satisfy mypy.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Zie619

src/ai_bom/utils/validator.py

@@ -6,15 +6,15 @@
 from pathlib import Path
 from typing import Any
 
-import jsonschema
 from jsonschema import validate
 
 
 def get_schema() -> dict[str, Any]:
     """Load the AI-BOM JSON schema."""
     schema_path = Path(__file__).parent.parent / "schema" / "bom-schema.json"
     with open(schema_path, encoding="utf-8") as f:
-        return json.load(f)
+        result: dict[str, Any] = json.load(f)
+        return result
 
 
 def validate_output(data: dict[str, Any]) -> None: