feat(engine): CC-6/7/8/10 M4 tokens, hop_legal, bundle, quantization

[soltrinox]

Summary

• CC-6: pluggable tokens.py counters for cost; packing keeps metrics.estimate_tokens
• CC-7: PersistentAgentHandle.hop_legal() false with pending tool state (+ docs/HOP_LEGAL.md)
• CC-8: bundle.py export_bundle/import_bundle round-trip (graph, lineage, ledger, tensors)
• CC-10: optional CHAT_COMPRESSOR_TENSOR_QUANT float16/int8 with reconstruction cosine budget

Branched from origin/main (CC-9 remains on PR #3 / compass/cc9-advisory-handoff — not included here).

Test plan

• cd engine && python -m pytest — 73 passed, 1 skipped (HF optional)
• Sanitize: no /Users/rosario in engine/src, engine/tests, docs
• CI green on this PR

Do not merge until reviewed.