fix: adjust detail ad slots and unify comment badges

[sdk-kr]

Summary

• remove in-content detail-page ads and keep the detail ad directly before comments
• remove the post-detail after-comments ad slot
• unify text-list comment badges to [n] format across board/feed/explore/groups
• add an explore period redesign spec for the cache-backed migration path

Verification

• pnpm exec eslint apps/web/src/routes/[boardId]/[postId]/+page.svelte apps/web/src/lib/components/features/board/layouts/view/basic.svelte apps/web/src/lib/components/features/board/layouts/view/report.svelte apps/web/src/lib/components/features/board/layouts/list/classic.svelte apps/web/src/lib/components/features/board/layouts/list/archive.svelte apps/web/src/routes/feed/+page.svelte apps/web/src/routes/explore/+page.svelte apps/web/src/routes/groups/+page.svelte apps/web/src/lib/utils/comment-count.ts

[github-actions]

Staging 배포 완료

URL: https://dev.damoang.net
이미지: staging-7566edd
Static Release: sha-7566edd
커밋: 7566edd

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