chore(scope): gate legacy integrations from onboarding runtime

[Aparnap2]

Context

Runtime profile onboarding_v6 enables exactly [slack, salesforce, jira, notion]. Legacy integrations (stripe, plaid, erpnext, hubspot, quickbooks) are archived and fail-closed via DisabledIntegrationError.

Branch state (do NOT reimplement)

Largely implemented on feature/ontologyai-onboarding-restructure (uncommitted): apps/ai/config/runtime.yaml + worker gating + apps/ai/config/archive/. This issue covers verification and commit only.

Scope

• Verify the default worker boots on onboarding_v6 and any attempt to invoke a legacy integration raises DisabledIntegrationError (fail-closed test, red first if missing).
• Verify the archive inventory is complete (every legacy integration accounted for, none importable from the onboarding path).
• Commit the config/worker/archive work on the branch.

Acceptance

• Fail-closed test green; ruff check clean; legacy code untouched (archived, not deleted).

Verification

• uv run pytest apps/ai/tests/ -k "legacy or disabled_integration or runtime_gating" -v (from apps/ai)

Supersedes

• #1 Foundation Hygiene #53 (Foundation Hygiene — mockoon port fix already landed in adf06a8, legacy gating done on this branch, /v6/status superseded by runtime.yaml worker gating).