v0.2.0 — offline benchmark

v0.2 — offline benchmark (milestone issues #6, #7, #11).

• amberfork-bench: the pre-registered chimera protocol (BENCHMARK.md) as a Rust harness —
  four arms (random, pos-lexical, nw-structural/resync, nw-lexical/resync) scored on identical
  fixtures with coverage accounting, Wilson 95% intervals, and a calibration curve; parameter
  freeze via bench/params.toml (every table names the config sha256); committed results
  documents + offline report mode that re-renders them with zero fetch.
• Mode A′ cross-system pairs, end-to-end in one binary: fetch (pinned upstream commits,
  licensing notices, provenance record) → TapeAgents reference adapter → build-pairs →
  scored disclosure. The honest result on the 4 constructible real pairs is a null
  (engine 0.50 ±3 vs random 0.75 — short runs, murky cross-system gold; both pre-registered
  threats) — shipped as a disclosed limit, not a headline (notebook 016).
• CI-visible fork-localization gate: GAIA-sanitized dev fixtures for seeds 42/43/44 committed
  under bench/fixtures/chimera_noise_seed*_dev/ with a full regeneration recipe;
  chimera_parity pins each seed's own baseline on every amberfork-align change (issue #11,
  notebooks 013–014).
• Honesty correction: the seed-42 0.75 exact headline was a favorable draw — README and the
  gate now lead with the cross-seed ±3 window and the 0.56 aggregate exact (notebook 014).
• First sealed test-split reveal (protocol rule 2, at this tag): dev-tuned params
  generalized — engine ±3 0.91 [0.78, 0.97] vs best baseline 0.49 [0.33, 0.64]
  (non-overlapping), exact 0.49 [0.33, 0.64] vs 0.00, on n=35 unseen pairs across three seeds;
  calibration monotone on unseen data; results committed with report snapshot tests
  (notebook 017).
• amberfork-ingest: warn when a trace declares a non-native schema version.
• Workspace version now single-sourced from [workspace.package] (0.2.0).