Add footer and improve layout structure

- Create Footer component with links to GitHub and Mastodon
- Restructure root layout with flex column for sticky footer
- Update OS layout to use flex-1 for proper height inheritance

src/app/layout.tsx

@@ -4,6 +4,7 @@ import { ThemeProvider } from "next-themes";
 import "./globals.css";
 
 import { NavTop } from "@/components/navtop";
+import { Footer } from "@/components/footer";
 import { Toaster } from "@/components/ui/sonner";
 import { Suspense } from "react";
 
@@ -34,11 +35,14 @@ export default function RootLayout({
         className={`${geistSans.variable} ${geistMono.variable} antialiased`}
       >
         <ThemeProvider attribute="class" defaultTheme="system" enableSystem>
-          <NavTop />
-          <Toaster />
-          <Suspense>
-            <main className="flex flex-col">{children}</main>
-          </Suspense>
+          <div className="flex flex-col min-h-screen">
+            <NavTop />
+            <Toaster />
+            <Suspense>
+              <main className="flex-1 flex flex-col">{children}</main>
+            </Suspense>
+            <Footer />
+          </div>
         </ThemeProvider>
       </body>
     </html>

src/app/os/layout.tsx

@@ -38,7 +38,7 @@ export default function OSDetailLayout({
   }, [os]);
 
   return (
-    <div className="flex flex-col h-[calc(100vh-56px)] p-4 md:p-6" suppressHydrationWarning>
+    <div className="flex flex-col flex-1 min-h-0 p-4 md:p-6" suppressHydrationWarning>
       <header className="flex flex-col sm:flex-row sm:items-center gap-2 mb-4 shrink-0">
         <div className="flex items-center gap-4">
           <Breadcrumb>

src/components/footer.tsx

@@ -0,0 +1,30 @@
+export function Footer() {
+  return (
+    <footer className="border-t border-border bg-muted/30 mt-auto">
+      <div className="px-4 md:px-8 py-6">
+        <div className="flex flex-col sm:flex-row items-center justify-between gap-4 text-sm text-muted-foreground">
+          <span>entdb</span>
+
+          <div className="flex items-center gap-4">
+            <a
+              href="https://github.com/chichou/entdb-indexer"
+              target="_blank"
+              rel="noopener noreferrer"
+              className="hover:text-foreground transition-colors"
+            >
+              GitHub
+            </a>
+            <a
+              href="https://infosec.exchange/@codecolorist"
+              target="_blank"
+              rel="noopener noreferrer"
+              className="hover:text-foreground transition-colors"
+            >
+              Mastodon
+            </a>
+          </div>
+        </div>
+      </div>
+    </footer>
+  );
+}