perf: optimize CI pipeline — eliminate double dependency installs, use local registry cache

- Frontend Dockerfile: split into deps/test/builder/nginx stages so npm ci
  runs once (cached when package-lock.json unchanged), tests run in build
- Backend Dockerfile: add test stage that runs pytest inside the build,
  eliminating separate test image build
- .drone.yml: remove separate test steps (now inside Dockerfile builds),
  point cache_from/cache_repo at local registry (10.0.20.10:5000) instead
  of Docker Hub for faster layer cache pulls

frontend/Dockerfile

@@ -1,22 +1,32 @@
-# Stage 1: Build the React app
-FROM node:24-alpine AS builder
+# Stage 1: Install dependencies (cached if package-lock.json unchanged)
+FROM node:24-alpine AS deps
 
 WORKDIR /app
 
 # Limit Node.js heap to avoid OOM in constrained CI environments
 ENV NODE_OPTIONS="--max-old-space-size=1024"
 
-# Copy package files first for better caching
+# Copy package files first for better layer caching
 COPY package.json package-lock.json* ./
 
 RUN npm ci
 
-# Copy all files and build
+# Stage 2: Run tests (fails the build if tests fail)
+FROM deps AS test
+
 COPY . .
 
-# Skip tsc type-checking (already done in test step); Vite transpiles via SWC
-RUN npx vite build 
+RUN npx vitest run
 
+# Stage 3: Build production bundle
+FROM deps AS builder
+
+COPY . .
+
+# Skip tsc type-checking (vitest already validated); Vite transpiles via SWC
+RUN npx vite build
+
+# Stage 4: Serve with nginx
 FROM nginx:alpine
 
 # Remove default nginx static files
@@ -24,9 +34,8 @@ RUN rm -rf /usr/share/nginx/html/*
 
 WORKDIR /app
 
-# Copy only necessary files from the builder stage
-COPY --from=builder /app/dist /usr/share/nginx/html  
-COPY --from=builder /app/nginx.conf /etc/nginx/conf.d/default.conf  
+COPY --from=builder /app/dist /usr/share/nginx/html
+COPY --from=builder /app/nginx.conf /etc/nginx/conf.d/default.conf
 
 EXPOSE 80
 CMD ["nginx", "-g", "daemon off;"]