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>

Dockerfile

@@ -1,3 +1,11 @@
+FROM node:20-slim AS frontend-build
+
+WORKDIR /build
+COPY frontend/package.json frontend/package-lock.json ./
+RUN npm ci
+COPY frontend/ ./
+RUN npm run build
+
 FROM python:3.12-slim
 
 WORKDIR /app
@@ -6,7 +14,7 @@ COPY backend/requirements.txt .
 RUN pip install --no-cache-dir -r requirements.txt
 
 COPY backend/ ./backend/
-COPY frontend/ ./frontend/
+COPY --from=frontend-build /build/dist ./frontend/
 
 ENV DB_PATH=/data/oil_calculator.db
 ENV FRONTEND_DIR=/app/frontend