feat(dialog): forward overlay props from content

[chahatkesh]

What

Adds an overlayProps escape hatch to DialogContent and AlertDialogContent in the current Base UI and Radix registry sources.

Why

Base UI intentionally omits backdrops for nested dialogs. Its Backdrop supports forceRender, but the shadcn convenience content components hardcoded their overlays, so consumers could not reach that prop without recomposing the portal and content.

Before this change, passing overlayProps leaked the unknown prop to the popup DOM node and a nested dialog still rendered only one backdrop. After the change, overlayProps={{ forceRender: true }} renders the nested backdrop while preserving Base UI's default behavior when the prop is omitted.

Changes

• forward overlayProps from Base UI Dialog and AlertDialog content to their overlays
• mirror the content API in the Radix registry sources to preserve base parity
• add jsdom regressions for nested Base UI Dialog and AlertDialog backdrops
• document the opt-in on the Base UI component pages

Verification

• pnpm exec vitest run apps/v4/registry/dialog.test.tsx (2 passed)
• NODE_OPTIONS=--max-old-space-size=4096 pnpm --filter=v4 typecheck
• pnpm --filter=v4 exec eslint registry/dialog.test.tsx registry/bases/base/ui/dialog.tsx registry/bases/base/ui/alert-dialog.tsx registry/bases/radix/ui/dialog.tsx registry/bases/radix/ui/alert-dialog.tsx
• pnpm exec prettier --check on all touched files
• pnpm --filter=v4 registry:build
• pnpm --filter=v4 postinstall

Reviewer notes

• Nested backdrop rendering remains opt-in; no default behavior changes.
• Related PR fix(dialog): allow custom overlay props when controlling open state #8732 targets the legacy new-york-v4/deprecated registries for overlay styling and also includes app bootstrap changes. This PR targets the current Base/Radix source registries, covers AlertDialog, and validates Base UI forceRender with tests and docs.

Closes #11214

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