Update path hash handling to accept variable-length hex-encoded hashes
(e.g. "4a" for single-byte, "b3fa" for multibyte) instead of requiring
exactly 2-character hashes. Bump meshcore dependency to >=2.3.0.
- Update normalizer to accept even-length hex strings >= 2 chars
- Update schemas and model docstrings for variable-length hashes
- Add tests for multibyte and mixed-length path hash round-trips
- Fix web test flakiness from local .env datetime locale leaking
