docs: align Quality Evaluation API with the current contract

[tn819]

Summary

• Pluralize the Quality Evaluation API to POST /v1/quality-evaluations and GET /v1/quality-evaluations/{job_id} (and matching poll_url).
• Remove poll summary / overall_score / granular_counts. Echo source, target, and glossary entries (source_entry, target_entry, ranges; omitted when empty). Document optional metadata.glossary_ids.
• Keep the pages off the public sidebar: Quality Evaluation is a hidden: true nav group (same pattern as Translate Audio Files). Closed-alpha callout unchanged. No changelog entry.

Test plan

• Confirm Mintlify sidebar does not show Quality Evaluation on the public API Reference tab
• Direct URLs /api-reference/quality-evaluation, /submit, /poll still resolve
• Generated OpenAPI Try it / examples use plural paths and a done body without summary
• Submit schema shows optional glossary_ids