examples: add local ART-E email task

[drsteinerdj]

Summary

• Add a local ART-E email-search task under examples/art_e_local
• Include deterministic inbox fixtures, search/read helpers, reward scoring, and a small ART Trajectory rollout adapter
• Add a lightweight notebook, README, and focused pytest coverage so the task contract can be reviewed without API keys, GPUs, W&B, or remote email infrastructure

Bounty fit

This targets the easy ART-E agent-task scope from the Prime Intellect ART-E / ART bounty:

https://algora.io/PrimeIntellect-ai/bounties/cxptwFoEv2up9Qjm

The core ART repo already had local ART-E example attempts, but maintainers noted examples now live in this repository. This PR puts the local ART-E task in OpenPipe/art-notebooks.

Verification

• python -m black examples\art_e_local
• python -m pytest examples\art_e_local\test_email_task.py -q -> 5 passed
• python -m py_compile examples\art_e_local\email_task.py examples\art_e_local\rollout.py examples\art_e_local\test_email_task.py
• python -m json.tool examples\art_e_local\art-e-local-task.ipynb
• python examples\art_e_local\email_task.py

Note: python -m ruff check examples\art_e_local could not be run in this global Python environment because ruff is not installed there.