CRUX M5: Advanced quantization — 10 missing stories

[noahgift]

Parent: #917

Scope

bitsandbytes / GPTQ / AWQ parity beyond the Q4_K/Q5_K/Q6_K/Q8_K already shipped.

Contracts in scope

• contracts/crux-B-{02,07,08,09,10,11,15,16,17,18}-v1.yaml

Exit criteria

• 10 contracts promoted missing → supported
• trueno kernels + apr quantize surface exposes new schemes
• Golden parity vs reference implementations within tolerance

Dependencies

• trueno SIMD kernels (crates/aprender-compute/)
• apr quantize CLI