Track 3Jane USD3 OC

[spalen0]

Summary

• add USD3 OC monitoring from sUSD3 subordination using Deployed / (Deployed - sUSD3)
• alert HIGH below 111% OC and CRITICAL below 106% OC. 3Jane OC target is 111.11% - https://app.3jane.xyz/info/backing
• document thresholds and cover OC alert behavior in tests

Tests

• uv run pytest -q tests/test_3jane.py
• uv run ruff check protocols/3jane/main.py tests/test_3jane.py tests/conftest.py
• git diff --check

Notes

• A targeted mypy run still hits existing shared utility typing issues in utils/formatting.py, utils/abi.py, and utils/web3_wrapper.py.