chore(frontend): enforce template interpolation layout

Co-authored-by: Codex <noreply@openai.com>

frontend/eslint.config.ts

@@ -1,5 +1,48 @@
 import antfu from '@antfu/eslint-config'
 
+const templateStylePlugin = {
+  rules: {
+    'single-line-simple-interpolation': {
+      meta: {
+        type: 'layout',
+        fixable: 'whitespace',
+        schema: [],
+        messages: {
+          expectedSingleLine: 'Expected a simple mustache interpolation to stay on one line.',
+        },
+      },
+      create(context) {
+        const { parserServices } = context.sourceCode
+        if (!parserServices.defineTemplateBodyVisitor)
+          return {}
+
+        return parserServices.defineTemplateBodyVisitor({
+          'VExpressionContainer[expression!=null]': function (node) {
+            if (node.parent.type !== 'VElement')
+              return
+
+            const expression = node.expression
+            if (
+              expression.loc.start.line !== expression.loc.end.line
+              || node.loc.start.line === node.loc.end.line
+            ) {
+              return
+            }
+
+            context.report({
+              node,
+              messageId: 'expectedSingleLine',
+              fix(fixer) {
+                return fixer.replaceText(node, `{{ ${context.sourceCode.getText(expression)} }}`)
+              },
+            })
+          },
+        })
+      },
+    },
+  },
+}
+
 export default antfu(
   {
     type: 'app',
@@ -18,4 +61,23 @@ export default antfu(
       a11y: true,
     },
   },
+  {
+    files: ['**/*.vue'],
+    plugins: {
+      'template-style': templateStylePlugin,
+    },
+    rules: {
+      'template-style/single-line-simple-interpolation': 'error',
+      'vue/html-closing-bracket-newline': ['error', {
+        singleline: 'never',
+        multiline: 'always',
+      }],
+      'vue/multiline-html-element-content-newline': ['error', {
+        ignores: ['pre', 'textarea'],
+        ignoreWhenEmpty: true,
+        allowEmptyLines: false,
+      }],
+      'vue/mustache-interpolation-spacing': ['error', 'always'],
+    },
+  },
 )