fix: remove frontend-builder stage, use pre-built webui/dist to avoid npm timeout on VPS

Dockerfile

@@ -1,10 +1,3 @@
-FROM node:20-alpine AS frontend-builder
-WORKDIR /build
-COPY webui/package*.json ./
-RUN npm install
-COPY webui/ .
-RUN npm run build
-
 FROM python:3.12-slim
 WORKDIR /app
 
@@ -16,7 +9,6 @@ COPY requirements.txt .
 RUN pip install --no-cache-dir -r requirements.txt
 
 COPY . .
-COPY --from=frontend-builder /build/dist /app/webui/dist
 
 RUN mkdir -p /app/logs