add Prettier config from nullcart.

Editor format-on-save uses root .prettierrc; align App.vue indentation.

.prettierrc

@@ -0,0 +1,13 @@
+{
+    "printWidth": 120,
+    "tabWidth": 4,
+    "useTabs": false,
+    "semi": true,
+    "singleQuote": true,
+    "trailingComma": "none",
+    "bracketSpacing": true,
+    "proseWrap": "never",
+    "htmlWhitespaceSensitivity": "strict",
+    "endOfLine": "lf",
+    "arrowParens": "avoid"
+}

frontend/src/App.vue

@@ -1,32 +1,32 @@
 <template>
-  <main class="home">
+    <main class="home">
-    <h1>Private Image</h1>
+        <h1>Private Image</h1>
-  </main>
+    </main>
 </template>
 
 <style scoped>
 .home {
-  box-sizing: border-box;
+    box-sizing: border-box;
-  min-height: 100vh;
+    min-height: 100vh;
-  margin: 0;
+    margin: 0;
-  padding: 2rem;
+    padding: 2rem;
-  font-family:
+    font-family:
-    system-ui,
+        system-ui,
-    -apple-system,
+        -apple-system,
-    Segoe UI,
+        Segoe UI,
-    Roboto,
+        Roboto,
-    sans-serif;
+        sans-serif;
-  line-height: 1.5;
+    line-height: 1.5;
 }
 
 h1 {
-  margin: 0 0 0.5rem;
+    margin: 0 0 0.5rem;
-  font-size: 1.75rem;
+    font-size: 1.75rem;
-  font-weight: 600;
+    font-weight: 600;
 }
 
 p {
-  margin: 0;
+    margin: 0;
-  color: #444;
+    color: #444;
 }
 </style>