feat(simply-aep): validate EntityDefinition eligibility for domain-process-binding SObject fields

[ClayChipps]

Summary

• Adds two new `simply aep at4dx domain-process-binding validate` rules that catch a class of wiring problem invisible to every existing rule: the wrong choice between `RelatedDomainBindingSObject__c` (the "primary" EntityDefinition-typed field) and `RelatedDomainBindingSObjectAlternate__c` (the plain-text "Alternate" field).
  • `unsupported-entity-definition-object` (error): the primary field is set to a standard object that can't actually go through an `EntityDefinition` metadata relationship (e.g. `ServiceResource`, `Task`) — this is a hard Setup/deploy failure with no fallback.
  • `unnecessary-entity-definition-alternate` (warning): the Alternate field is set to an object that's actually eligible (e.g. `Account`, or any custom object) — nothing's broken (AT4DX unions both fields at runtime), but it's the wrong field choice.
• Both check against a new maintained internal allowlist (`ENTITY_DEFINITION_STANDARD_OBJECTS`), not a live org `describe` call, so `--source-dir`-only validation stays fully connection-free, consistent with every other rule in this command.
• Full design rationale, alternatives considered (including why an org-describe-based check was rejected), and the allowlist's best-effort/non-authoritative status are in docs/design/0014.

Test plan

• New unit tests in `simply-aep-core` covering both rules, including the two ways they interact with the existing `ambiguous-sobject-reference` rule (co-occur vs. never co-occur).
• Fixed two `simply-aep` command test fixtures and one `simply-aep-core` write test fixture that incidentally exercised the exact misuse these new rules now (correctly) flag.
• Full `simply-aep-core` and `simply-aep` test suites pass locally (pre-existing, unrelated `simply-data` fixture failures aside).
• `pnpm run readme` regenerated for `simply-aep-core`, `simply-aep`, and the `simply` orchestrator (which bundles `simply-aep`); `pnpm --filter site run sync` regenerated the two affected docs-site pages.
• `pnpm run build` passes for all three packages (lint, compile, command-snapshot).

Co-Authored-By: Claude Sonnet 5 noreply@anthropic.com

https://claude.ai/code/session_014oTGUGohBiqrzETHCs25AB