Improve GAM slot stability and refresh cadence

[sdk-kr]

Summary

• reduce GAM auto refresh interval from 60s to 30s
• reserve responsive ad slot heights up front to reduce CLS
• stop recalculating slot min-height only after client mount

Validation

• pnpm --dir /home/angple/web/apps/web run check
• pnpm --dir /home/angple/web/apps/web exec eslint src/lib/components/ui/ad-slot/ad-slot.svelte src/lib/config/ad-config.ts
• full lint was attempted, but repo-wide eslint did not finish promptly in this environment; CI should confirm the full workflow

[github-actions]

Staging 배포 완료

URL: https://dev.damoang.net
이미지: staging-3da9838
Static Release: sha-3da9838
커밋: 3da9838

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