Add Fin Agent API orchestration endpoints to v2.14, v2.15, and v2.16

Document the `/fin/capabilities`, `/fin/ask`,
`/fin/procedures/{procedure_id}/run`, and `/fin/escalate` endpoints on API
versions 2.14, 2.15, and 2.16. Update the Fin Agent tag description to list
these endpoints, and add `intercom_conversation_id` to the `/fin/ask` and
`/fin/procedures/{procedure_id}/run` responses.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EExbnyABqRELbKq47qWL3q

Author: rahulgdsouza