Serve the static search index with compression and quality guardrails

[next-devin]

Problem

The generated merchant-docs search index is useful to agents, but production serves the multi-megabyte JSON payload without an explicit JSON content type or compressed transfer guarantee. Query relevance is also unguarded.

Acceptance criteria

• Serve /api/search as JSON with browser MIME-sniffing disabled.
• Keep the raw index within a documented ceiling and add a realistic Brotli transfer-size budget.
• Add CI checks for representative subscription, payment-gateway, and webhook queries.
• Keep the checks tied to the exported Orama index rather than a separate fixture.

Verification

• Production build succeeds.
• Search size and query-quality checks pass in CI.
• After deployment, response headers confirm JSON content type and compressed delivery.