[Performance] Investigate performance of GET /cloud-api/folders

GET /cloud-api/folders has frequent long response times, which makes Cloud Page loading and folder navigation feel slow.
Please profile this endpoint and identify optimization opportunities.

Focus:

• Measure latency across proxy, backend, DB, and filesystem.
• Check for expensive recursion, N+1 queries, and missing indexes (user_id, parent_id).
• Propose concrete improvements with expected impact.

Acceptance Criteria

• Baseline latency metrics documented (including p95).
• Primary bottleneck(s) identified with evidence.
• Clear optimization plan (or implementation) delivered.

Labels
performance, backend, cloud-page, api, investigation