docs(onboarding): re-author prose that named removed types

[ivanball]

Summary

Follow-up to #219. The last 26 dead in-guide anchors named types that no longer exist in source. The prose around them sat in sections the type-drift pipeline never reopens (the section's own type was unchanged), so it described code that is gone. 15 parts were re-authored from current source:

• Scoring pipeline (Conference domain, application, infrastructure, UI overview, testing rollup): now describes the durable internal command, ScoreEventSessionsInternalCommandHandler plus SessionScoringRunner, instead of ScoreEventSessionsHandler, AnthropicScoringService, SessionScoringProcessor and SessionScoringQueue.
• ValReturn<T>, FakeRefreshSessionStore, AdministrationRequestValidators, CacheKeyPrefix, EventValidationRules and DuplicateKeyDetection references rewritten from source or dropped.
• devops-aspire: the AppHost composition smoke-test section rewritten for the current tier (AdcAppHostSmokeTests on Common's AppHostFixtureBase).
• 99-coverage-audit.md: the 2026-09-26 note records the follow-up.

Verification

• verify.ps1: exit 0. 0 missing, 0 rollup contract failures, 0 citation failures, 0 anchor failures, rubric 34/34.
• test-verify.ps1: 33 passed, 0 failed.
• Evidence spot-check: 4 CONFIRMED, 2 DRIFTED on framing only (an intended rollup subsection the unit charter does not list; an author evidence row that is not a cite in the prose). Every sampled claim verified.
• npm run build: dead cross-links none.

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