fix(referral-traffic): order Traffic Insights sources cdn-first

[cwjwisse]

What

Flips the Traffic Insights source-ordering so the has-data endpoint returns availableSources cdn-first instead of optel-first.

src/controllers/llmo/llmo-referral-traffic.js:

• TRAFFIC_INSIGHTS_SOURCES = ['optel', 'cdn'] → ['cdn', 'optel'] (the derived TRAFFIC_INSIGHTS_TABLES follows in lockstep).
• Updated the rationale comment block and the has-data JSDoc to describe cdn as the preferred source.

Why

Referral Traffic Insights has two mutually-exclusive sources per site (optel & cdn). Product rule: always prefer cdn over optel. Clients (referral dashboard, agentic, url-inspector) read availableSources[0] as the active source, so ordering has-data cdn-first makes all of them seed cdn over optel for free.

AA / GA4 / CJA are unaffected — they live in the separate Business Impact tab and use their own DRS provider check. The has-data availableSources is type-locked to 'optel' | 'cdn' only.

Scope / not changed

• The filter-dimensions availableSources path is untouched — it comes from the RPC row.available_sources, a different code path independent of this constant.

Merge order

⚠️ Merge this BEFORE the frontend PR. The frontend reads availableSources[0]; until this lands it degrades gracefully to optel.

Test

• npx mocha test/controllers/llmo/llmo-referral-traffic.test.js → 89 passing (flipped the has-data both-records assertion to ['cdn', 'optel']).
• eslint on changed files clean.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[MysticatBot]

Hey @cwjwisse,

⚠ Degraded review - no spec document was found for this change (searched the PR links, the touched repos' docs, the architecture/guidelines docs, and linked Jira). This review covers code-level quality but could not validate the change against an agreed design, so confidence is reduced. Add a spec link (PR template section 4) and re-request review for a full-confidence pass.

Verdict: Approve - clean, well-scoped config flip with matching test coverage.
Changes: reorders the Traffic Insights source priority array from optel-first to cdn-first so clients prefer cdn as the active data source (2 files).

No issues found. The constant reorder, derived table mapping, comment updates, and test assertion all move in lockstep. No logic paths are affected beyond output ordering since TRAFFIC_INSIGHTS_TABLES is derived via .map from the same array.

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