Add optional replay game flow

[Spbd1]

Motivation

• Provide an optional second decision-only playthrough after the full study flow so behavioral replay data can be collected without repeating surveys.
• Ensure replay choices are stored separately from the original run and include assignment logic that either preserves or flips the hidden profile for analysis.
• Expose replay results in the local export, validation schema, and admin CSV so replay behavior-change metrics are available for downstream analysis.

Description

• Added a new route /replay-game and reused the existing HiddenCostGame component in mode="replay" to run a replay-only game (UI copy clarifies that no surveys will be repeated).
• Implemented replay state creation and assignment with createReplayGameState that randomly picks assignmentCondition of "same-hidden-profile" or "switched-hidden-profile" while preserving displayedProfile and setting hiddenProfile and treatmentCostMultiplier accordingly.
• Persisted replay state under replayGame (type ReplayGameState) in ResearchSession and updated buildResearchExport to include replayGame, added replayGameSchema to Zod validation, and extended ComputedResearchMetrics with replay/behavior-change fields such as replayAvailable, replayCompleted, replayAssignmentCondition, behaviorChangeFullTreatment, and behaviorChangeCostBurden.
• Added an export-side prompt with the button text "Play one more round sequence" and guidance about submission behavior, updated the participant-facing ResultsTable to surface replay metrics, and extended admin CSV columns to include replay and change metrics for downstream analysis.

Testing

• Ran type checking with npm run typecheck and it completed successfully.
• Ran lint with npm run lint which passed aside from an existing ParticipantBackgroundForm.tsx react-hooks/exhaustive-deps warning.
• Built the project with npm run build which completed successfully and produced the site routes including /replay-game.
• Validated export schema with npm run validate:sample which succeeded after updating the sample fixture and schema to include the new replay fields.

---

Codex Task