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/composables/useDialog.js

@@ -0,0 +1,43 @@
+import { reactive } from 'vue'
+
+export const dialogState = reactive({
+  visible: false,
+  type: 'alert', // 'alert', 'confirm', 'prompt'
+  message: '',
+  defaultValue: '',
+  resolve: null
+})
+
+export function showAlert(msg) {
+  return new Promise(resolve => {
+    dialogState.visible = true
+    dialogState.type = 'alert'
+    dialogState.message = msg
+    dialogState.resolve = resolve
+  })
+}
+
+export function showConfirm(msg) {
+  return new Promise(resolve => {
+    dialogState.visible = true
+    dialogState.type = 'confirm'
+    dialogState.message = msg
+    dialogState.resolve = resolve
+  })
+}
+
+export function showPrompt(msg, defaultVal = '') {
+  return new Promise(resolve => {
+    dialogState.visible = true
+    dialogState.type = 'prompt'
+    dialogState.message = msg
+    dialogState.defaultValue = defaultVal
+    dialogState.resolve = resolve
+  })
+}
+
+export function closeDialog(result) {
+  dialogState.visible = false
+  if (dialogState.resolve) dialogState.resolve(result)
+  dialogState.resolve = null
+}