Refactor frontend to Vue 3 + Vite + Pinia + Cypress E2E

- Replace single-file 8441-line HTML with Vue 3 SPA
- Pinia stores: auth, oils, recipes, diary, ui
- Composables: useApi, useDialog, useSmartPaste, useOilTranslation
- 6 shared components: RecipeCard, RecipeDetailOverlay, TagPicker, etc.
- 9 page views: RecipeSearch, RecipeManager, Inventory, OilReference, etc.
- 14 Cypress E2E test specs (113 tests), all passing
- Multi-stage Dockerfile (Node build + Python runtime)
- Demo video generation scripts (TTS + subtitles + screen recording)

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

frontend/src/main.js

@@ -0,0 +1,10 @@
+import { createApp } from 'vue'
+import { createPinia } from 'pinia'
+import App from './App.vue'
+import router from './router'
+import './assets/styles.css'
+
+const app = createApp(App)
+app.use(createPinia())
+app.use(router)
+app.mount('#app')