Allow installing this app as a Web App (#419)

* added an icon of 512x512 for the manifest

* added a web app manifest

* added a screenshot for richer install on mobile

* added a screenshot for richer install ui on desktop

* added a document to include the manifest

* fixed the command to generate a better auth secret

* moved the link tag directly into the PageHead component

apps/web/src/components/PageHead.tsx

@@ -8,6 +8,7 @@ export const PageHead = ({ title }: { title: string }) => {
         name="viewport"
         content="width=device-width, initial-scale=1, maximum-scale=1"
       />
+      <link rel="manifest" href="/manifest.json" />
     </Head>
   );
 };