refactor: improve JSON parsing reliability with json-repair library

Replace regex-based JSON extraction with json-repair for better handling of malformed LLM responses. Remove deprecated JSON parsing utilities and clean up keyword_extraction parameter across LLM providers.

- Remove locate_json_string_body_from_string() and convert_response_to_json()
- Use json-repair.loads() in extract_keywords_only() for robust parsing
- Clean up LLM interfaces and remove unused parameters
- Add json-repair dependency

pyproject.toml

@@ -66,6 +66,7 @@ api = [
     "httpcore",
     "httpx",
     "jiter",
+    "json-repair",
     "passlib[bcrypt]",
     "psutil",
     "PyJWT",