v0.7.0 - ops/CLI wave, KD tokenizer guard, benchmark negative results

Retroactive cut of the Oct 28 afternoon wave.

New CLI surface (replaces the ad-hoc host scripts)

• brainforge ops status / ops log: run-state and log inspection with encoding fallback (#64)
• brainforge dataset filter --sidecar (#64) and dataset split --sidecar (#65)
• brainforge pipeline kd-pass: per-case KD generation with resume, per-case timeout, sidecar-aligned assembly (#66)
• brainforge config set / config set-model (#67)
• brainforge train evaluate --base: base-model perplexity, comparable numbers (#64)
• brainforge providers check-logprobs: KD teacher signal probe (#72)
• brainforge train runs: summary table over every run (#73)

KD science + guard

• Benchmark negative results documented: a cross-tokenizer teacher drove the student to 20.07 ppl (worse than the 12.61 baseline); bimodal loss curve; tokenizer-family guard warns before training (#68, #69, #70).