Search: make the Filters block's InnerBlocks boundary obvious in the editor (#50655)

* Search: make the Filters block's InnerBlocks boundary obvious in the editor

A new filter dropped near the bottom of the sidebar Filters block can
land as a sibling in the parent column instead of a child inside its
InnerBlocks region — it silently falls out of the composition (no sync
to Collapsible Filters, no sidebar styling) with nothing in the editor
to flag it. Add a bounded appender, a labeled dashed-outline boundary,
and a warning Notice when a filter block ends up stray. Same treatment
for Filters Product.

* Search: drop the stray-filter warning notice

The bounded appender and labeled boundary are enough to prevent and
surface the mis-nesting on their own; the extra warning notice added
noise without clear benefit.

* Address review: match Product Filters boundary label to block.json title

* Address review: fix AGENTS.md section pointer and changelog block name

Committed via a GitHub action: https://github.com/Automattic/jetpack/actions/runs/29723462885

Upstream-Ref: Automattic/jetpack@eb69497

Author: kangzj

dist/index.d.cts

@@ -1852,7 +1852,7 @@ declare const BaseTooltip: ({
   className,
   style,
   renderContainer
-}: BaseTooltipProps) => string | number | true | import("react/jsx-runtime").JSX.Element | Iterable<ReactNode>;
+}: BaseTooltipProps) => string | number | true | Iterable<ReactNode> | import("react/jsx-runtime").JSX.Element;
 //#endregion
 //#region src/components/tooltip/accessible-tooltip.d.ts
 type FlattenedTooltipData = {

dist/index.d.ts

@@ -1852,7 +1852,7 @@ declare const BaseTooltip: ({
   className,
   style,
   renderContainer
-}: BaseTooltipProps) => string | number | true | import("react/jsx-runtime").JSX.Element | Iterable<ReactNode>;
+}: BaseTooltipProps) => string | number | true | Iterable<ReactNode> | import("react/jsx-runtime").JSX.Element;
 //#endregion
 //#region src/components/tooltip/accessible-tooltip.d.ts
 type FlattenedTooltipData = {