[pm-rahulsengupta]

What

Adds an optional AHREFS_API_KEY env that enriches domain overview results
with the free Ahrefs public Domain Rating (/v3/public/domain-rating-free).

• src/server/lib/ahrefs/client.ts — small key-gated client for the free
  endpoint; parses the endpoint's nested
  {"domain_rating": {"domain_rating": <0-100>}} payload (flat form also
  accepted) with Zod range validation, retries once with a date param if
  the API demands one, and never throws into the overview flow
• DomainService — fetches the rating in parallel with the paid DataForSEO
  call (Promise.allSettled), stores it on the 12h-cached overview object
• get_domain_overview MCP tool — returns ahrefsDomainRating when present
• Domain overview UI — an "Ahrefs DR" stat when the value is present
• compose/env-example/preflight plumbing, same pattern as other optional keys

Why

Domain overview is the app's most-used research entry point, and its metrics
all charge DataForSEO credits. Ahrefs' public Domain Rating endpoint is free
with a free-tier API key, so self-hosters get a domain-strength signal at
zero marginal cost. Without the key the feature is off and nothing changes.

The Ahrefs call bypasses billing entirely: no credits, no metering, and a
failure degrades to a null field without affecting the DataForSEO result.

Testing

Unit tests for the client (key-gated skip, the endpoint's real nested payload
shape, flat shape, date retry, 403, unparseable and out-of-range payloads),
tsc --noEmit clean, and type-aware lint clean on the changed files.

[pm-rahulsengupta]

Running on our self-hosted instance — the optional Ahrefs free Domain Rating shows up in domain overview as designed. Available for any review feedback.