fix(service): normalize public ingestion errors

[charlesbluca]

Description

Normalize ingestion failures once before they reach public status responses, callback logs, and ingest metrics. This prevents string-backed GraphIngestionError values from being rendered character-by-character and adds an optional redacted error_details payload (type, stage, endpoint, message) while retaining the compatible error string.

The regression coverage includes plain strings, lists, generic exceptions, nested OCR HTTP 422 failures, redaction, and status/metrics consistency.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

Documentation is not required: this is an internal/public error-rendering compatibility fix with self-contained API fields.