v0.16.0

Rule receipts — the per-rule verdict card (community-suggested).

• New /warden-receipt command (npx tsx src/receipt.ts [--agent <name>] [--json]) renders the evidence behind each keep/evict decision as one card:
  token savings vs. context rent (with variance and ROI multiple), the model and
  golden-suite hash it was measured under, per-task pass/fail with vs. without
  the rule, and the tool-call / file-reread activity profile with vs. without
  (shown as a signed % so a reviewer can see whether a "cheap" rule did less
  work). Read-only; the natural payload for sharing a rule — "my delta is
  evidence, not authority for your repo."
• The selector now records a receipt snapshot (rule_receipts table, migration
  #9) at every decision — initial and each re-audit, so a rule has an audit
  trail. The keep/evict verdict logic is unchanged; receipts are additive
  capture. RunResult now carries tool-call / file-reread counts; bench.ts
  gains goldenSuiteHash for suite provenance.
• The safety axis is surfaced, not auto-judged: a big activity drop is usually
  the point of an efficiency rule, so the receipt shows the numbers and leaves
  the call to a human — the binding safety gate remains the per-task pass/fail
  regression, which evicts on its own.
• 292 tests, green on Node 22 and 24.