feat(web): page-driven breadcrumb context + header render + objects wiring (#54)

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

web/src/shell/breadcrumb-provider.tsx

@@ -0,0 +1,12 @@
+import { useState, type ReactNode } from "react";
+
+import { BreadcrumbContext, type BreadcrumbItem } from "./breadcrumb-context";
+
+export function BreadcrumbProvider({ children }: { children: ReactNode }) {
+  const [trail, setTrail] = useState<BreadcrumbItem[]>([]);
+  return (
+    <BreadcrumbContext.Provider value={{ trail, setTrail }}>
+      {children}
+    </BreadcrumbContext.Provider>
+  );
+}