feat: comprehensive boilerplate improvements

Security & Stability:
- Add Next.js 16 proxy.ts for BetterAuth cookie-based auth protection
- Add rate limiting for API routes (src/lib/rate-limit.ts)
- Add Zod validation for chat API request bodies
- Add session auth check to chat and diagnostics endpoints
- Add security headers in next.config.ts (CSP, X-Frame-Options, etc.)
- Add file upload validation and sanitization in storage.ts

Core UX Components:
- Add error boundaries (error.tsx, not-found.tsx, chat/error.tsx)
- Add loading states (skeleton.tsx, spinner.tsx, loading.tsx files)
- Add toast notifications with Sonner
- Add form components (input.tsx, textarea.tsx, label.tsx)
- Add database indexes for performance (schema.ts)
- Enhance chat UX: timestamps, copy-to-clipboard, thinking indicator,
  error display, localStorage message persistence

Polish & Accessibility:
- Add Open Graph and Twitter card metadata
- Add JSON-LD structured data for SEO
- Add sitemap.ts, robots.ts, manifest.ts
- Add skip-to-content link and ARIA labels in site-header
- Enable profile page quick action buttons with dialogs
- Update Next.js 15 references to Next.js 16

Developer Experience:
- Add GitHub Actions CI workflow (lint, typecheck, build)
- Add Prettier configuration (.prettierrc, .prettierignore)
- Add .nvmrc pinning Node 20
- Add ESLint rules: import/order, react-hooks/exhaustive-deps
- Add stricter TypeScript settings (exactOptionalPropertyTypes,
  noImplicitOverride)
- Add interactive setup script (scripts/setup.ts)
- Add session utility functions (src/lib/session.ts)

All changes mirrored to create-agentic-app/template/

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/app/layout.tsx

@@ -1,9 +1,10 @@
-import { ThemeProvider } from "@/components/theme-provider";
-import type { Metadata } from "next";
 import { Geist, Geist_Mono } from "next/font/google";
 import "./globals.css";
-import { SiteHeader } from "@/components/site-header";
 import { SiteFooter } from "@/components/site-footer";
+import { SiteHeader } from "@/components/site-header";
+import { ThemeProvider } from "@/components/theme-provider";
+import { Toaster } from "@/components/ui/sonner";
+import type { Metadata } from "next";
 
 const geistSans = Geist({
   variable: "--font-geist-sans",
@@ -16,9 +17,62 @@ const geistMono = Geist_Mono({
 });
 
 export const metadata: Metadata = {
-  title: "Agentic Coding Boilerplate",
+  title: {
+    default: "Agentic Coding Boilerplate",
+    template: "%s | Agentic Coding Boilerplate",
+  },
   description:
     "Complete agentic coding boilerplate with authentication, database, AI integration, and modern tooling - perfect for building AI-powered applications and autonomous agents by Leon van Zyl",
+  keywords: [
+    "Next.js",
+    "React",
+    "TypeScript",
+    "AI",
+    "OpenRouter",
+    "Boilerplate",
+    "Authentication",
+    "PostgreSQL",
+  ],
+  authors: [{ name: "Leon van Zyl" }],
+  creator: "Leon van Zyl",
+  openGraph: {
+    type: "website",
+    locale: "en_US",
+    siteName: "Agentic Coding Boilerplate",
+    title: "Agentic Coding Boilerplate",
+    description:
+      "Complete agentic coding boilerplate with authentication, database, AI integration, and modern tooling",
+  },
+  twitter: {
+    card: "summary_large_image",
+    title: "Agentic Coding Boilerplate",
+    description:
+      "Complete agentic coding boilerplate with authentication, database, AI integration, and modern tooling",
+  },
+  robots: {
+    index: true,
+    follow: true,
+  },
+};
+
+// JSON-LD structured data for SEO
+const jsonLd = {
+  "@context": "https://schema.org",
+  "@type": "WebApplication",
+  name: "Agentic Coding Boilerplate",
+  description:
+    "Complete agentic coding boilerplate with authentication, database, AI integration, and modern tooling",
+  applicationCategory: "DeveloperApplication",
+  operatingSystem: "Any",
+  offers: {
+    "@type": "Offer",
+    price: "0",
+    priceCurrency: "USD",
+  },
+  author: {
+    "@type": "Person",
+    name: "Leon van Zyl",
+  },
 };
 
 export default function RootLayout({
@@ -28,6 +82,12 @@ export default function RootLayout({
 }>) {
   return (
     <html lang="en" suppressHydrationWarning>
+      <head>
+        <script
+          type="application/ld+json"
+          dangerouslySetInnerHTML={{ __html: JSON.stringify(jsonLd) }}
+        />
+      </head>
       <body
         className={`${geistSans.variable} ${geistMono.variable} antialiased`}
       >
@@ -38,8 +98,9 @@ export default function RootLayout({
           disableTransitionOnChange
         >
           <SiteHeader />
-          {children}
+          <main id="main-content">{children}</main>
           <SiteFooter />
+          <Toaster richColors position="top-right" />
         </ThemeProvider>
       </body>
     </html>