Refactor worker parse contract boundaries

[suguanYang]

Summary

• replace worker parse and URL upload contract tests with real Celery task entrypoints and boundary observations
• add filesystem-backed object storage for contract runtime instead of LocalStack/Docker
• let worker parsing recover job context from Postgres, persist processing metadata durably, and reject oversized PDFs before parser execution

Verification

• uv run pytest apps/worker/tests/contract -q
• .venv/bin/ruff check apps packages
• .venv/bin/pyright --project pyproject.toml apps/worker/app apps/worker/worker.py packages/shared-python/shared

Note: full-repo Pyright still reports existing unrelated API route errors in apps/api/app/api/v1/routes/retrieval.py:90-92.