docs(bf-4q2): update plan.md - stale Status table, module layout, and undocumented watchdog/flags
- Update Status table: main() session orchestration COMPLETE (shipped as v0.2.0), E2E tests now reference bead bf-46x
- Add missing files to Module Layout: src/check.rs, lib.rs, poller.rs, session.rs, watchdog.rs; tests/hooks.rs, stop_poller.rs, pty_integration.rs, integration.rs, watchdog.rs; build.rs; scripts/ directory; CI YAMLs
- Document watchdog component (section 10): no-output/max-turn/stop-hook timeout monitoring with TimeoutType enum and WatchdogConfig
- Add watchdog CLI flags to table: --first-output-timeout, --stream-json-timeout, --stop-hook-timeout
- Update stream-json description: note current implementation is post-session replay, live tailing tracked as bead bf-5vm
- Make Phase 1 --version text version-agnostic
- Renumber Install Script section from 11 to 12
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