fix(Dockerfile): build frontend without NODE_ENV=production (npm skips devDeps like vite -> 'vite: not found')

Root cause of EasyPanel build failure: ENV NODE_ENV=production was set before 'npm install',
so npm skipped devDependencies (vite, @vitejs/plugin-vue) and 'npm run build' had no vite.
Fix: remove the early NODE_ENV=production (devDeps install for the build), use 'npm ci'
(deterministic, falls back to npm install). NODE_ENV only matters for Flask runtime which is set
at the CMD stage.

Dockerfile

@@ -8,12 +8,12 @@ RUN apt-get update \
   && apt-get install -y --no-install-recommends nodejs \
   && rm -rf /var/lib/apt/lists/*
 
-ENV NODE_ENV=production
 WORKDIR /app
 
-# 1) Build frontend
+# 1) Build frontend (devDeps incl. vite are required to build;
+#    NODE_ENV must NOT be production yet or npm skips devDependencies)
 COPY frontend/package.json frontend/package-lock.json* ./frontend/
-RUN cd frontend && npm install
+RUN cd frontend && npm ci || npm install
 COPY frontend/ ./frontend/
 RUN cd frontend && npm run build