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

Dockerfile

@@ -28,7 +28,7 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     libmariadb3 \
     && rm -rf /var/lib/apt/lists/*
 
-# Stage 3: Test image — runtime deps + venv + test dependencies
+# Stage 3: Test — runtime deps + venv + test dependencies + run tests
 FROM runtime-base AS test
 
 WORKDIR /app
@@ -38,6 +38,10 @@ ENV PATH="/app/.venv/bin:$PATH"
 
 RUN pip install --no-cache-dir pytest pytest-asyncio pytest-xdist httpx aioresponses fakeredis
 
+COPY . .
+
+RUN pytest tests/ -x -q
+
 # Stage 4: Final image — combine venv from builder + runtime base
 FROM runtime-base