docs: add AGENTS.md agent operating guidance

[andrewluxem]

Summary

• Adds a self-contained, vendor-neutral AGENTS.md for TorchTrade.
• Keeps the tracked change to one docs-only file.
• Respects the existing repo convention that CLAUDE.md and .claude/ are git-ignored local maintainer tooling.

Repo tailoring

• Treats TorchTrade as a shared, multi-maintainer OSS RL-for-trading library.

• Adds explicit financial/trading safety boundaries:

  • no live trading
  • no order placement
  • no broker/exchange or account mutations
  • no portfolio changes
  • no real-money execution
  • no investment advice, trading recommendations, guaranteed-return language, or performance claims

• Names protected risk surfaces:

  • broker/exchange credentials
  • .env and credential variables
  • datasets and generated outputs
  • model artifacts and checkpoints
  • notebooks
  • trading logs
  • live and paper trading adapters
  • external-service integrations such as wandb, Hugging Face, OpenAI/vLLM/LLM calls

• Documents approval-gated commands and actions:

  • uv sync
  • uv run pytest
  • mkdocs serve
  • model training
  • backtests
  • data downloads
  • live/paper broker or exchange calls

• Notes the existing @claude GitHub Action reads AGENTS.md, so AGENTS.md is the appropriate vendor-neutral shared agent guidance file.

Validation

• Confirmed only AGENTS.md was committed.
• Confirmed CLAUDE.md and .claude/ remain ignored/untracked and were not force-added.
• Confirmed no source, tests, examples, package/config files, workflows, datasets, model artifacts, notebooks, generated outputs, trading logs, runtime files, or secrets changed.
• Confirmed git diff --cached --check was clean before commit.
• Confirmed no real credential values were introduced; policy words and placeholder variable names only.

Safety

• Docs-only change.
• No install, test, training, backtest, data download, broker/exchange call, order placement, live trading, external API, release, publish, deploy, or automation action was run.
• No secrets, .env values, broker/exchange keys, account balances, portfolio data, private datasets, generated private outputs, or trading logs were inspected or printed.
• No financial advice, performance claim, guaranteed-return language, trading recommendation, or investment recommendation was added.