v4.20.0 — measure delegation drift

Added

• /cli-dispatch:drift reports delegation drift between injected policy and actual runner use.
  The new read-only report counts recent deterministic runner sessions, raw worker sessions,
  policy-injected Claude Code transcripts, Anthropic Agent spawns, inline Edit/Write
  tool use, and Bash invocations of cli-dispatch-run or /cli-dispatch:run. It keeps
  transcript scanning cheap by filtering JSONL files by mtime before reading them and by
  counting with text scans rather than JSON parsing, making the "policy arrived but behaviour
  did not change" failure mode visible without dumping transcript contents.