Add delayed-reveal experimental condition with pre-reveal reflection

[Spbd1]

Motivation

• Introduce a hidden experimental variation that randomizes whether participants see the hidden-rule reveal immediately or after a brief, neutral reflection period.
• Capture a short commitment rating and optional free-text reflection before revealing the hidden rule for delayed participants so the experiment can measure persistence of initial interpretations.
• Assignment must be applied only after completing the pre-reveal survey so existing sessions that never submit the pre-reveal step remain unchanged.

Description

• Add new types and fields: RevealTimingCondition and PreRevealCommitment and expose revealTimingCondition and preRevealCommitment on ResearchSession and ResearchExport in types/research.ts and include delayedReveal and standByInitialInterpretation in computed metrics.
• Persist randomized assignment at pre-reveal submit with assignRevealTimingCondition in utils/session.ts, update components/PreRevealSurveyForm.tsx to call it when needed and branch the next navigation to either /hidden-rule-reveal or /pre-reveal-reflection based on the assigned condition.
• Add the reflection UI and route: components/PreRevealReflectionForm.tsx implements the neutral message, required 1–7 Likert (standByInitialInterpretation) and optional trimmed text (<=500 chars), and app/pre-reveal-reflection/page.tsx provides the page shell; components/HiddenRuleReveal.tsx guards to redirect delayed participants to the reflection page if they try to open the reveal early.
• Export/schema/admin updates: include revealTimingCondition and preRevealCommitment in the final research export via utils/researchMetrics.ts, validate them in lib/researchExportSchema.ts, and add CSV columns reveal_timing_condition, stand_by_initial_interpretation, and pre_reveal_commitment_text in lib/adminSubmissions.ts.

Files changed (high-level): types/research.ts, utils/session.ts, components/PreRevealSurveyForm.tsx, components/PreRevealReflectionForm.tsx (new), app/pre-reveal-reflection/page.tsx (new), components/HiddenRuleReveal.tsx, utils/researchMetrics.ts, lib/researchExportSchema.ts, lib/adminSubmissions.ts.

Testing

• Ran npm run typecheck and it completed successfully with no new type errors.
• Ran npm run lint and it completed; the run reported existing react-hooks/exhaustive-deps warnings in ParticipantBackgroundForm.tsx and PostRevealSurveyForm.tsx that were present before this change.
• Ran npm run build and the Next.js production build completed successfully and generated the new static page for /pre-reveal-reflection.

All automated checks passed; no new lint errors or type errors were introduced (only preexisting lint warnings remained).

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Codex Task