add manifest

frontend/src/assets/app.webmanifest

@@ -0,0 +1,26 @@
+{
+  "theme_color": "#52a756",
+  "background_color": "#121212",
+  "icons": [
+    {
+      "purpose": "maskable",
+      "sizes": "512x512",
+      "src": "image/icon512_maskable.png",
+      "type": "image/png"
+    },
+    {
+      "purpose": "any",
+      "sizes": "512x512",
+      "src": "image/icon512_rounded.png",
+      "type": "image/png"
+    }
+  ],
+  "start_url": "/",
+  "orientation": "portrait",
+  "display": "standalone",
+  "dir": "auto",
+  "lang": "en-US",
+  "name": "Picsur",
+  "short_name": "Picsur",
+  "description": "An easy to use, selfhostable image sharing service"
+}

frontend/src/index.html

@@ -7,6 +7,8 @@
       href="/assets/branding/logo/picsur.svg"
       type="image/svg+xml"
     />
+    <link rel="manifest" href="/assets/app.webmanifest">
+    <meta name="theme-color" content="#52a756" />
 
     <base href="/" />
     <meta name="viewport" content="width=device-width, initial-scale=1" />