Add frontend CI workflow, error boundary, and VITE_API_URL support

- .github/workflows/frontend.yml: type-check + build on push/PR
- ErrorBoundary component wraps App with catch + retry UI
- API client reads VITE_API_URL env var for non-same-origin deploys
- vite-env.d.ts declares ImportMetaEnv type

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.github/workflows/frontend.yml

@@ -0,0 +1,37 @@
+name: Frontend CI
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - 'frontend/**'
+      - '.github/workflows/frontend.yml'
+  pull_request:
+    branches: [main]
+    paths:
+      - 'frontend/**'
+      - '.github/workflows/frontend.yml'
+  workflow_dispatch:
+
+concurrency:
+  group: frontend-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: frontend
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '22'
+          cache: 'npm'
+          cache-dependency-path: frontend/package-lock.json
+
+      - run: npm ci
+      - run: npx tsc --noEmit
+      - run: npm run build

frontend/src/api/client.ts

@@ -1,6 +1,6 @@
 import type { ModelInfo, SavingsData, ServerInfo } from '../types';
 
-const BASE = '';  // relative to same origin
+const BASE = import.meta.env.VITE_API_URL || '';  // relative to same origin by default
 
 export async function fetchModels(): Promise<ModelInfo[]> {
   const res = await fetch(`${BASE}/v1/models`);

frontend/src/components/ErrorBoundary.tsx

@@ -0,0 +1,86 @@
+import { Component } from 'react';
+import type { ErrorInfo, ReactNode } from 'react';
+
+interface Props {
+  children: ReactNode;
+}
+
+interface State {
+  hasError: boolean;
+  error: Error | null;
+}
+
+export class ErrorBoundary extends Component<Props, State> {
+  constructor(props: Props) {
+    super(props);
+    this.state = { hasError: false, error: null };
+  }
+
+  static getDerivedStateFromError(error: Error): State {
+    return { hasError: true, error };
+  }
+
+  componentDidCatch(error: Error, info: ErrorInfo) {
+    console.error('ErrorBoundary caught:', error, info.componentStack);
+  }
+
+  render() {
+    if (this.state.hasError) {
+      return (
+        <div style={styles.container}>
+          <div style={styles.card}>
+            <h2 style={styles.heading}>Something went wrong</h2>
+            <p style={styles.message}>
+              {this.state.error?.message || 'An unexpected error occurred.'}
+            </p>
+            <button
+              style={styles.button}
+              onClick={() => this.setState({ hasError: false, error: null })}
+            >
+              Try again
+            </button>
+          </div>
+        </div>
+      );
+    }
+    return this.props.children;
+  }
+}
+
+const styles: Record<string, React.CSSProperties> = {
+  container: {
+    display: 'flex',
+    alignItems: 'center',
+    justifyContent: 'center',
+    height: '100vh',
+    backgroundColor: '#1a1a1e',
+    color: '#e2e8f0',
+    fontFamily: '-apple-system, BlinkMacSystemFont, "Segoe UI", system-ui, sans-serif',
+  },
+  card: {
+    textAlign: 'center' as const,
+    padding: 32,
+    maxWidth: 420,
+  },
+  heading: {
+    fontSize: 20,
+    fontWeight: 600,
+    marginBottom: 12,
+  },
+  message: {
+    fontSize: 14,
+    color: '#94a3b8',
+    marginBottom: 24,
+    lineHeight: 1.5,
+  },
+  button: {
+    padding: '10px 24px',
+    borderRadius: 8,
+    border: 'none',
+    backgroundColor: '#2563eb',
+    color: 'white',
+    fontSize: 14,
+    fontWeight: 500,
+    cursor: 'pointer',
+  },
+};

frontend/src/main.tsx

@@ -1,10 +1,13 @@
 import { StrictMode } from 'react';
 import { createRoot } from 'react-dom/client';
+import { ErrorBoundary } from './components/ErrorBoundary';
 import App from './App';
 import './App.css';
 
 createRoot(document.getElementById('root')!).render(
   <StrictMode>
-    <App />
+    <ErrorBoundary>
+      <App />
+    </ErrorBoundary>
   </StrictMode>,
 );

frontend/src/vite-env.d.ts

@@ -0,0 +1,9 @@
+/// <reference types="vite/client" />
+
+interface ImportMetaEnv {
+  readonly VITE_API_URL: string;
+}
+
+interface ImportMeta {
+  readonly env: ImportMetaEnv;
+}