PM-5396: Surface AI Engineering stats history

[jmgasper]

What was broken
AI-tagged Data Science challenges could have AI Engineering aggregate stats without matching AI Engineering history rows, so profile challenge details could not render them under Development > AI Engineering while preserving the native Data Science > Challenge history.

Root cause
The member stats history fallback only synthesized missing native track/type pairs. Configured rating path aggregate pairs were ignored, and the challenge metadata used by history fallback did not include tags or skills needed to match rating path configuration.

What was changed
Loaded challenge tags and skills for history fallback metadata. Added configured rating path history synthesis for missing aggregate pairs from review results and challenge winner rows when the challenge matches the configured rating path.

Any added/updated tests
Added coverage for Data Science challenges tagged AI to remain under DATA_SCIENCE.Challenge history while also appearing under DATA_SCIENCE["AI Engineering"] history for the profiles app to render under Development > AI Engineering.

Validation:

• pnpm exec mocha -t 20000 test/unit/StatisticsService.test.js --exit
• pnpm lint
• pnpm build attempted, but this repo does not define a build script
• pnpm test attempted; with dummy DB URLs it ran 146 non-DB tests successfully and failed only DB-backed MemberService/MemberTraitService hooks because no PostgreSQL server is available at localhost:5432
• Non-DB unit suite excluding MemberService.test.js and MemberTraitService.test.js passed with 146 tests