fix(openmemory): prevent multilingual simhash collisions across JS and Python

[zfaustk]

Summary

This fixes the multilingual simhash collision path behind #147 across both OpenMemory runtimes.

• extend tokenization to retain CJK runs instead of dropping them as non-ASCII noise
• expand CJK tokens into bigrams so distinct Chinese inputs no longer collapse into the same empty token set
• fall back to a stable text hash when tokenization yields nothing, instead of returning the same all-zero simhash
• add matching JS and Python regression coverage for Chinese inputs and punctuation-only inputs

Fixes #147.

Testing

• cd packages/openmemory-py && pytest -q tests/test_multilingual_dedup.py
• cd packages/openmemory-js && timeout 20s npx --yes tsx tests/test_multilingual_dedup.ts

Notes

• The JS regression assertions completed and printed test_multilingual_dedup.ts passed, but the process kept lingering handles alive afterward, so I wrapped that check with timeout 20s for this run.
• I intentionally left packages/openmemory-js/package-lock.json out of this patch because the only change was incidental install churn, not source behavior.