Differentiate floor 3 and 4 world reactions

[SilverSupplier]

Summary

• Add floor-specific world reactions so floor 3 creates visible flow bridge spans while floor 4 stabilizes hazards and advances the safe reset point.
• Change floor 4's first stabilizer to reuse Earth + SteelBrace, making the same combo read as bridge support on floor 3 and crack stabilization on floor 4.
• Require overlay/combo casts to touch the matching world-goal area before completion, so shared combos must be drawn near the intended floor target.
• Add PlayMode coverage for the same-combo interpretation split, local goal targeting, and safe-point update.

Related Issues

• Closes: [Child #17] 3층/4층 world reaction 차별화 #50
• Related: [Unity] 5층 final seal challenge와 층별 연출 polish #17, Feat: tune Magic Exam Hall world casting timing #58, Strengthen final floor guidance and ending #63
• Follow-up:

Merge Order

• Preferred: merge Feat: tune Magic Exam Hall world casting timing #58 first, then rebase or re-check this PR because Feat: tune Magic Exam Hall world casting timing #58 also tightens world-cast timing and goal targeting.
• If this PR lands before Feat: tune Magic Exam Hall world casting timing #58, re-check Feat: tune Magic Exam Hall world casting timing #58 because both touch WorldStateGoal.MatchesOverlay and nearby PlayMode smoke coverage.
• Strengthen final floor guidance and ending #63 is functionally separate, but it also edits ExamGameController.cs and PlayMode smoke tests, so whichever lands second should resolve and re-run checks.

Verification

• node scripts/validate-doc-state.mjs
• Unity PlayMode tests: 7 passed
• Unity EditMode tests: 19 passed
• GitHub checks observed after latest push: validate-docs, build, test, and CodeQL passed.
• npm test; Not run locally, Unity-only change and local node_modules is not installed.
• npm run build; Not run locally, Unity-only change and local node_modules is not installed.

Notes

• Scope: Unity floor 3/4 world reactions, floor copy, hazard stabilization behavior, localized world-goal completion, and PlayMode regression coverage.
• Out of scope / follow-up: manual playtest observation write-up and broader final-floor polish.
• Risk notes: floor 4 now asks for Earth + SteelBrace for the first stabilizer, which is intentional reuse after floor 3 teaches that combo. Localized goal completion reduces the risk of a central cast completing a distant floor objective.

Review Checklist

• This PR changes user-facing UI or behavior.
• This PR changes recognizer behavior.
• This PR changes docs, task state, or project process.
• This PR changes ML artifacts, datasets, generated outputs, or capture/export behavior.
• This PR changes logging, survey fields, privacy, or research data handling.
• This PR needs screenshots or a short playtest note.

Screenshots / Playtest Notes

Batchmode PlayMode confirms Earth + SteelBrace no longer completes the floor 3 bridge from the room center, then reads as a flow bridge near the floor 3 target and as a hazard stabilizer/safe point near the floor 4 crack.