Add Prettier for TypeScript formatting

- Install prettier
- Configure .prettierrc.json and .prettierignore
- Add npm scripts: format, format:check
- Add Makefile target: format-frontend
- Format all frontend files

frontend/app/login/page.tsx

@@ -41,7 +41,9 @@ export default function LoginPage() {
             {error && <div style={styles.error}>{error}</div>}
 
             <div style={styles.field}>
-              <label htmlFor="email" style={styles.label}>Email</label>
+              <label htmlFor="email" style={styles.label}>
+                Email
+              </label>
               <input
                 id="email"
                 type="email"
@@ -54,7 +56,9 @@ export default function LoginPage() {
             </div>
 
             <div style={styles.field}>
-              <label htmlFor="password" style={styles.label}>Password</label>
+              <label htmlFor="password" style={styles.label}>
+                Password
+              </label>
               <input
                 id="password"
                 type="password"