Phase 10: JSON/JSONL support in both operators
- ReadOperator: output_type="json" now writes JSON array, added "jsonl" for JSONL
- WriteOperator: file input defaults to JSONL, source_type="json" for JSON array
- Added read_jsonl_file(), renamed write_json_file() to write_jsonl_file()
- New write_json_file() for JSON array format

Phase 11: Overwrite clear_mode parameter
- Added clear_mode="sheet" (default): clears entire sheet + trims extra rows
- Added clear_mode="range": clears only data columns, leaves neighbours intact
- Added trim_sheet() to GoogleSheetsHook
- Fixed: overwrite no longer leaves stale data below new export

Updated READMEs (EN/RU), examples, CHANGELOG.