CI: guard references/*.md extension-type + uipath.* claims against bpmn-spec.json (from #3217/#3225 reviews)

[nikhil-maryala]

Context

From @rockymadden's #3217/#3225 reviews. Three PRs in a row shipped a named absolute about extension types that was wrong (uipath.aggregate "doesn't exist" — it's a Jint helper; "only X/Y have a template" — StartAgentJob etc. exist; Orchestrator.RunJob called an extension type — it's an outputType). Each was caught at review, not CI.

Fix

Add a CI check (extend tests/tasks/uipath-maestro-bpmn/_shared/test_bpmn_check.py, which already asserts doc claims against bpmn-spec.json) that:

1. Extracts Namespace.Type tokens (e.g. Orchestrator.StartJob, Actions.HITL) and uipath.* helper tokens from skills/uipath-maestro-bpmn/references/**/*.md.
2. For any token asserted to not exist (or asserted as an extension type), checks it against bpmn-spec.json extensionTypes / uipathShortcuts and the Jint-helper allowlist.
3. Fails when a doc negates an identifier the spec defines, or calls an outputType an extension type.

Acceptance

A false absolute about an extension type / Jint helper in the references fails CI instead of surfacing in review.