fix(lint): resolve 4 ruff CI failures (#14)

- core/mesh/__init__.py: sort import block (I001) and __all__ list (RUF022)
- core/mesh/credit_ledger.py:443: remove redundant utf-8 arg from .encode() (UP012)
- core/mesh/task_router.py:108: remove quotes from LocalNodeRegistry | None annotation (UP037)

Co-authored-by: Mustworkharder <nordbitio@gmail.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: 3 people