fix docker build: use npm for vite build stage

Bun's node_modules layout causes resolution failures when Node/Vite
tries to load modules. Use npm install + npx vite build for
reliable frontend builds, keep Bun for runtime.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Dockerfile

@@ -1,8 +1,7 @@
 FROM node:22-slim AS build
 WORKDIR /app
-RUN npm install -g bun
-COPY package.json bun.lock* ./
-RUN bun install --frozen-lockfile
+COPY package.json ./
+RUN npm install
 COPY . .
 RUN npx vite build