test(client): unit + smoke coverage for API-parity additions

Two pieces:

1. tests/test_api_parity.py — 40 mock-driven unit tests covering:
   - `_post`/`_patch` json kwarg aliases
   - resolve / validate (POST endpoints) request shape + response parsing
   - WebhookAlert CRUD (create / update / list)
   - WebhookEndpoint create/update with name= (and DeprecationWarning
     when name= is omitted)
   - WebhookSubscription create with endpoint=, subscription_type=,
     filter fields
   - ordering= threading on the seven affected list_* methods
   - Reference-data and entity/agency sub-resource URL construction

2. scripts/smoke_api_parity.py — live smoke test that hits every method
   the branch added or changed against a running Tango. Skips
   gracefully when the local server can't service a particular
   endpoint (404 for attachment-search without the RAG index; 504 from
   funding-contracts aggregation; alerts can't auto-resolve endpoint
   when the test user owns multiple). Creates webhook endpoints +
   subscriptions, verifies them, and tears them down. Local run on
   2026-05-11: 45/45 PASS (with three SKIPs for the environmental
   reasons above).

Also includes a trivial ruff-format collapse in models.py
(VEHICLE_ORDERS_MINIMAL one-liner).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: infinityplusone