docs(bf-1v8): fix README exit codes and sync flags table, add docs/notes stubs
- Fix exit-code table: change incorrect codes 3/4 to correct values 124 (timeout) and 130 (interrupted), matching src/error.rs implementation
- Add missing timeout flags to flags table: --first-output-timeout (90s), --stream-json-timeout (90s), --stop-hook-timeout (120s), matching src/cli.rs defaults
- Add docs/notes/hook-design.md covering relay hook mechanics, FIFO protocol, and keeper fd pattern (from src/hook.rs, src/poller.rs)
- Add docs/notes/terminal-probes.md covering Ink probe table and response bytes (from src/terminal.rs)
Co-Authored-By: Claude <noreply@anthropic.com>
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