fix(builder): sanitize non-string style values + allowlist element tags (XSS)

Adversarial re-review found the C1 fix incomplete plus an adjacent
same-class XSS, both reachable via the AI update_props path and
deserialized saved state:

- cssPropsToString only ran sanitizeCssValue on typeof-string values, so a
  non-string style value (array/object) with a valid key skipped
  sanitization entirely and was template-coerced raw into style="...",
  e.g. { color: ['red', '"><img src=x onerror=alert(1)>'] }. Now every
  non-number value is coerced with String() and sanitized; numbers stay
  raw. sanitizeBreakoutChars also now escapes < and > (previously only ;
  and ") as defense-in-depth, since values can reach it from non-string
  sources.

- props.tag (Container) and props.level (Heading) were interpolated raw
  into the tag position of exported HTML (`<${tag}`, `<${level}`) with no
  runtime validation, letting a malicious value break out of the tag
  entirely. Both are now allowlisted/clamped against their known-safe sets
  (div/section/article/header/footer/main; h1-h6), falling back to
  div/h2. Applied in Container's live render + toHtml, Heading's live
  render + toHtml, and the typeName==='div' fallback branch in
  html-export.ts's renderNode (hit for unresolved/legacy node types).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

craft/src/components/layout/Container.tsx

@@ -3,6 +3,19 @@ import { useNode, UserComponent } from '@craftjs/core';
 import { cssPropsToString } from '../../utils/style-helpers';
 import { escapeAttr } from '../../utils/escape';
 
+// The only tag names Container actually supports (matches the TS union
+// below and the `tag` default in `.craft.props`). `tag` is settable via the
+// AI `update_props` path and from deserialized saved state -- neither is
+// type-checked at runtime -- so a malicious value like
+// `div><img src=x onerror=alert(1)` must never reach the `<${tag}` template
+// position in `toHtml`/the live render. Anything not in this allowlist
+// falls back to `'div'`.
+const ALLOWED_CONTAINER_TAGS = ['div', 'section', 'article', 'header', 'footer', 'main'] as const;
+export type ContainerTag = (typeof ALLOWED_CONTAINER_TAGS)[number];
+
+export const sanitizeContainerTag = (tag: unknown): ContainerTag =>
+  (ALLOWED_CONTAINER_TAGS as readonly unknown[]).includes(tag) ? (tag as ContainerTag) : 'div';
+
 interface ContainerProps {
   style?: CSSProperties;
   tag?: 'div' | 'section' | 'article' | 'header' | 'footer' | 'main';
@@ -42,6 +55,7 @@ export const Container: UserComponent<ContainerProps> = ({
 }) => {
   const { connectors: { connect, drag } } = useNode();
 
+  const safeTag = sanitizeContainerTag(tag);
   const needsBoxedWrapper = contentWidth === 'boxed';
   const flexStyles = flexAlignFromTextAlign(style.textAlign);
 
@@ -58,7 +72,7 @@ export const Container: UserComponent<ContainerProps> = ({
   const idValue = cssId || anchorId || undefined;
 
   const el = React.createElement(
-    tag,
+    safeTag,
     {
       ref: (ref: HTMLElement | null): void => { if (ref) connect(drag(ref)); },
       style: outerStyle,
@@ -97,7 +111,7 @@ Container.craft = {
 /* ---------- HTML export ---------- */
 
 (Container as any).toHtml = (props: ContainerProps, childrenHtml: string) => {
-  const tag = props.tag || 'div';
+  const tag = sanitizeContainerTag(props.tag);
   const isBoxed = props.contentWidth === 'boxed';
   const flexStyles = flexAlignFromTextAlign(props.style?.textAlign);