feat: hide entry content from list, add GET /api/entries/:id/content endpoint

Content is no longer returned in the entries list. A separate endpoint
returns plain text content for clipboard copying on demand.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/vite.config.ts

@@ -0,0 +1,7 @@
+import { defineConfig } from 'vite'
+import react from '@vitejs/plugin-react'
+
+// https://vite.dev/config/
+export default defineConfig({
+  plugins: [react()],
+})