v0.46.0

Five roadmap features in one release: windup doctor (static preflight — LLM key, browser, scenarios, fragment orphans, site map); sharding (run --all --shard i/n across CI runners); accessibility audit (run --a11y, axe-core on the final page, informational — opt-in optional dep); flake root-cause hints (each flaky scenario gets a likely-cause hint); and run <id> --watch (re-run on file change). Each tested and validated live.