v2.2.0 — summarize skill

Added

• summarize skill (#60) — a probabilistic extractive summarizer: ranks content blocks by salience and takes the top ones verbatim (so the auto-judge sees grounded output), reporting a confidence. On a retry it takes fewer, stronger sentences, so a low-confidence first attempt recovers — exercising the full reliability layer (confidence routing → auto-judge → retry-with-negative-context) from a second skill (previously only extract-highlights did).
• State gains a DocSummary type + summary? field; new doc-summary@1.0 registry schema (additive), pinned as the skill's output_schema; a runnable examples/summarize.ts.