Restructure blogs as Astro monorepo

sites/research/src/components/elements/header-link.tsx

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+import { type ComponentProps } from "react";
+import { cn } from "@/lib/utils";
+
+type HeaderLinkProps = ComponentProps<"a">;
+
+export default function HeaderLink({
+  className,
+  children,
+  ...props
+}: HeaderLinkProps) {
+  return (
+    <a
+      {...props}
+      className={cn(
+        "inline-block text-blue-600 hover:text-blue-800 dark:text-blue-400 dark:hover:text-blue-200",
+        className,
+      )}
+    >
+      {children}
+    </a>
+  );
+}

sites/research/src/components/elements/theme-toggle.tsx

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+import { Moon, Sun } from "lucide-react";
+import { useEffect, useState } from "react";
+
+import { Button } from "@/components/ui/button";
+import { cn } from "@/lib/utils";
+
+const ThemeToggle = ({ className }: { className?: string }) => {
+  const [theme, setTheme] = useState<"light" | "dark">("light");
+
+  useEffect(() => {
+    // Get initial theme from localStorage or system preference
+    const savedTheme = localStorage.getItem("theme");
+    const systemTheme = window.matchMedia("(prefers-color-scheme: dark)")
+      .matches
+      ? "dark"
+      : "light";
+    const initialTheme = savedTheme || systemTheme;
+
+    setTheme(initialTheme as "light" | "dark");
+    document.documentElement.classList.toggle("dark", initialTheme === "dark");
+  }, []);
+
+  const toggleTheme = () => {
+    const newTheme = theme === "light" ? "dark" : "light";
+    setTheme(newTheme);
+    document.documentElement.classList.toggle("dark");
+    localStorage.setItem("theme", newTheme);
+  };
+
+  return (
+    <Button
+      variant="outline"
+      size="icon"
+      className={cn("size-8", className)}
+      onClick={toggleTheme}
+    >
+      <Sun className="size-4 rotate-0 scale-100 transition-all dark:-rotate-90 dark:scale-0" />
+      <Moon className="absolute size-4 rotate-90 scale-0 transition-all dark:rotate-0 dark:scale-100" />
+      <span className="sr-only">Toggle theme</span>
+    </Button>
+  );
+};
+
+export { ThemeToggle };