No pipeline observability endpoint or metrics export

[haydenk]

Problem

There is no way for operators to see the current state of the pipeline (last successful run, documents in queue, failed documents, row counts) without querying the database directly. The API has a /health endpoint that only returns ok, with no pipeline status information.

Expected behavior

Add a GET /status endpoint (or expand /health) that returns:

• Last completed run timestamp per TDSP and file type
• Count of documents in each status (discovered, downloaded, processing, completed, failed)
• Total active ESIID count
• Any documents currently stuck in processing

This gives operators a quick at-a-glance health check without needing database access.