Action-tier catalog doc

[SSBrouhard]

Goal

Create docs/action_catalog.md as a reviewer-readable tier model for VMGA actions.

Boundary

The catalog must be derived from, or asserted against, the real GmailAction classification and baseline_denies in code. It must not become a parallel narrative that reviewers believe is active while the adapter ignores it. That divergence is the exact hazard VMGAPolicy.validate_rules is meant to prevent.

Acceptance sketch

• Catalog maps actions to tiers using the shipped GmailAction classification and policy defaults.
• A test or release check asserts the doc stays aligned with code and baseline_denies.
• The doc names which controls are enforced by code versus deployment/operator policy.
• No new action tier is documented unless the adapter and policy validator understand it.

[SSBrouhard]

Created as a scoped follow-up from approval-signing design PR #27. Keep this catalog derived from real GmailAction classification and baseline_denies, not a parallel narrative.

[SSBrouhard]

Scope update (adversarial review triage, 2026-06-10): the action-tier catalog must classify label abuse, attachment downloads, and filter/forwarding rules as named exfiltration/risk vectors, derived from the real GmailAction classification + baseline_denies in code and asserted by a test (not a parallel narrative). State precisely what gogcli no-send + allowlist already covers. Cross-ref #1.