test: timestamp contract captures at runtime

[justinjoy]

Summary:

• record capture provenance with the actual UTC date
• keep paired live query and extraction captures on one timestamp
• preserve injectable timestamps for focused test coverage

Attempted an Ollama qwen3:8b capture using only the repository synthetic Acme prompts. Query intent parsed, but extraction failed at the production parse boundary; no partial fixtures are included.

Verification:

• .venv/bin/python -m pytest -q tests/contract/test_contract_meta.py
  • 50 passed
• provider-free replay nodes
  • 3 passed
• git diff --check

Related to #271