Add cost visibility condition before reveal

[Spbd1]

Motivation

• Introduce a pre-reveal cost-visibility experimental condition so participants receive varied levels of cost-related context on the /visible-results page without revealing the hidden-profile mapping (to study effects on attribution and later revision).
• Persist the assigned condition in the session and include it in exports and computed metrics for analysis while preserving compatibility with older sessions.

Description

• Data model: added CostVisibilityCondition and costVisibilityCondition?: { condition: "no-cost-info" | "partial-cost-hint" | "full-cost-preview"; assignedAt: string } to ResearchSession and ResearchExport, plus computed metric fields costVisibilityCondition, hadAnyCostHint, and hadStrongCostHint in ComputedResearchMetrics and exports; bumped schema version to hidden-cost-game-research-schema-5.
• Assignment: assign a random condition (1/3 each) when reaching the visible-results stage using assignCostVisibilityCondition in utils/session.ts (triggered from components/ResultsTable.tsx), and persist it in local storage; existing sessions without the field remain supported.
• UI: show a non-identifying pre-reveal note in ResultsTable via a new CostVisibilityNote component: no UI change for no-cost-info, a neutral hint for partial-cost-hint, and a stronger pre-reveal hint for full-cost-preview (both avoid revealing profile mapping).
• Exports & schema: included costVisibilityCondition in the research export, updated Zod lib/researchExportSchema.ts to validate the field and the new metric fields, added CSV columns in lib/adminSubmissions.ts (top-level cost_visibility_condition and metric columns metric_cost_visibility_condition, had_any_cost_hint, had_strong_cost_hint).
• Files changed: types/research.ts, utils/session.ts, components/ResultsTable.tsx, utils/researchMetrics.ts, lib/researchExportSchema.ts, lib/adminSubmissions.ts.

Testing

• Ran npm run typecheck — passed.
• Ran npm run lint — passed; reported an existing React Hook dependency warning in components/ParticipantBackgroundForm.tsx that pre-existed this change.
• Ran npm run build — production build succeeded and pages compiled (same existing lint warning reported).

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Codex Task