Feat: tune Magic Exam Hall world casting timing

[SilverSupplier]

Summary

• Tune world casting timing for steadier multi-stroke spell input.
• Extend default base seal lifetime so players have more room to attach overlays.
• Apply playable drawing defaults from both runtime setup and scene builder, and document the updated Unity controls.
• Add Unity EditMode/PlayMode coverage for timing defaults, seal lifetime, and nearby world-goal casting behavior.

Verification

• Unity EditMode tests: 20 passed
• Unity PlayMode tests: 6 passed
• node scripts/validate-doc-state.mjs
• GitHub build, test, validate-docs, and codeql checks

Notes

• This PR is scoped to world-casting timing and goal proximity tuning for [Child #13] world drawing buffer와 seal 유지시간 튜닝 #35.
• Overlay/base feedback copy changes are intentionally handled in separate PRs.

Closes #35
Refs #13