docs: list all worker signals and inject TypeError in README

[lesnik512]

Summary

The README said setup_di only uses worker_process_init/worker_process_shutdown, and the inject row omitted its decoration-time TypeError.

Evidence:

• modern_di_celery/main.py:39-40 also connects worker_init/worker_shutdown, the only signals the threads/gevent/eventlet pools send (comment at :29-36).
• modern_di_celery/main.py:68-75: inject raises TypeError when the task declares *args/**kwargs.

Changes

• Usage paragraph, eager-mode note, and setup_di row mention both signal pairs.
• inject row documents the TypeError.
• Remove the dash in the eager-mode note.
• Footer: "with IoC container" -> "with an IoC container", and the org-profile line no longer uses a dash.

Checklist

• Lint and format pass (ruff)
• Type check passes (ty)
• Tests pass and new behavior is covered
• Build succeeds (uv build) if packaging or build config changed
• Repo metadata stays consistent across the three surfaces (GitHub description, pyproject description, profile blurb) if this touches packaging

Docs-only change. just lint-ci and just test pass; no mkdocs.yml in this repo.