Make AI overview block fill width inside flex/grid Group blocks

When hamelp/ai-overview is placed in a WP Group block using flex layout
(e.g. alongside an "AIは間違うことがあります" disclaimer), the block root
collapsed to its intrinsic content width because flex Groups default their
children to size-to-content rather than stretch. Add width:100% (plus
box-sizing:border-box) to the .hamelp-ai-overview root so the form,
input-row and textarea inherit full width; no-op in normal block flow.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RCRKyC4sroy5Xk144DGJdS

Author: claude

src/blocks/ai-overview/style.scss

@@ -15,6 +15,13 @@
  */
 
 :where(.hamelp-ai-overview) {
+	// Fill the available width in every layout context. WordPress flex Group
+	// blocks default their children to size-to-content (align-items is not
+	// `stretch`), which otherwise collapses the block to its intrinsic width when
+	// placed alongside e.g. a disclaimer paragraph. width:100% keeps it full-width
+	// in flex/grid parents while remaining a no-op in normal block flow.
+	width: 100%;
+	box-sizing: border-box;
 	// Theme-aware tokens (override these from your theme to re-skin the block).
 	--hamelp-accent: var(--wp--preset--color--primary, #1571da);
 	--hamelp-on-accent: var(--wp--preset--color--base, #fff);