feat(email): add operator safety knobs

[guivernl]

Summary

• add EMAIL_DRAFT_MODE=1 to save generated email replies to Drafts instead of sending immediately
• add EMAIL_DISPLAY_NAME for a friendly outbound From header
• add optional per-sender hourly rate limiting via EMAIL_RATE_LIMIT_PER_HOUR
• add regression tests for each knob

Why

These are opt-in operator controls for deployments that expose the email gateway. They make unattended email operation easier to stage safely without changing defaults for existing installs.

Test plan

• uv run --with pytest --with pytest-asyncio python -m pytest tests/gateway/test_email.py -q -o 'addopts='

[teknium1]

Thanks for the concrete operator-safety work and regression coverage. The draft-review workflow is a legitimate need, but this implementation uses a configuration mechanism the project does not accept.

This automated hermes-sweeper review is closing the PR under the standing configuration policy:

• The PR makes three new non-secret behavioral environment variables (EMAIL_DRAFT_MODE, EMAIL_DISPLAY_NAME, and EMAIL_RATE_LIMIT_PER_HOUR) its public interface. Repository policy requires feature flags, display preferences, and thresholds to be configured through config.yaml rather than .env (AGENTS.md:102-107).
• The related draft-only PR feat(gateway): add EMAIL_SUPPRESS_OUTBOUND kill switch for draft-only mailboxes #5717 was closed for the same env-var-for-config policy direction.
• The patch also targets the former gateway/platforms/email.py; email now lives at plugins/platforms/email/adapter.py after 5600105478ffde29d7566b45421b100eaa29c4ef.

A focused follow-up using platforms.email config settings and covering all current email egress paths would be the supported direction.

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Closed as not-planned per standing maintainer policy (env-var-for-config). This is a design-direction decision, not a code-quality judgment — see the Contribution Rubric in AGENTS.md for what the project is looking for. If you believe this policy was misapplied to your change, comment here and a maintainer will take a look.