fix: resolve TS18046 errors for React 19 element props type

React 19 types React.ReactElement props as unknown instead of any. Test
helper functions that access element.props.children, .className, or .href
need explicit props type parameters on React.ReactElement and isValidElement.

Changes:
- admin/PublicShell.test.ts: add WithChildren type, use React.ReactElement<WithChildren>
- dashboard/PublicShell.test.ts: same pattern for childTypes and contentWrapper
- dashboard/StatCard.test.ts: add ElementWithClass type for className access
- dashboard/public-auth-pages.test.ts: add ElementWithHref type for href access

No any, @ts-ignore, or type assertion bypass used.

apps/dashboard/src/app/public-auth-pages.test.ts

@@ -19,10 +19,12 @@ function collectText(node: unknown): string[] {
   return [];
 }
 
+type ElementWithHref = { children?: React.ReactNode; href?: string; embedded?: boolean }
+
 function findElement(
   node: unknown,
-  predicate: (element: React.ReactElement) => boolean,
-): React.ReactElement | null {
+  predicate: (element: React.ReactElement<ElementWithHref>) => boolean,
+): React.ReactElement<ElementWithHref> | null {
   if (node === null || node === undefined || typeof node === "boolean")
     return null;
   if (Array.isArray(node)) {
@@ -32,7 +34,7 @@ function findElement(
     }
     return null;
   }
-  if (!isValidElement<{ children?: React.ReactNode }>(node)) return null;
+  if (!isValidElement<ElementWithHref>(node)) return null;
   if (predicate(node)) return node;
   return findElement(node.props.children, predicate);
 }