Refactor codebase following Clean Code principles and add 229 tests

- Extract helpers to reduce function sizes (listing_tasks, app.py, query.py, listing_fetcher)
  - Replace nonlocal mutations with _PipelineState dataclass in listing_tasks
  - Fix bugs: isinstance→equality check in repository, verify_exp for OIDC tokens
  - Consolidate duplicate filter methods in listing_repository
  - Move hardcoded config to env vars with backward-compatible defaults
  - Simplify CLI decorator to auto-build QueryParameters
  - Add deprecation docstring to data_access.py
  - Test count: 158 → 387 (all passing)

.claude/skills/build-and-push.md

@@ -0,0 +1,113 @@
+---
+name: build-and-push
+description: |
+  Build Docker images for the API and frontend, and push them to Docker Hub.
+  Use when: (1) user wants to build new Docker images locally, (2) push images
+  to the registry before deploying, (3) tag images for a release. Covers both
+  the Python/FastAPI backend and the React/Nginx frontend.
+author: Claude Code
+version: 1.0.0
+date: 2026-02-06
+---
+
+# Build and Push Docker Images
+
+All commands run locally. Images are pushed to Docker Hub under the `viktorbarzin` namespace.
+
+## Image Registries
+
+| Component | Docker Hub repo                    | Dockerfile location          |
+|-----------|------------------------------------|------------------------------|
+| API       | `viktorbarzin/realestatecrawler`   | `crawler/Dockerfile`         |
+| Frontend  | `viktorbarzin/immoweb`             | `crawler/frontend/Dockerfile`|
+
+## Building Images
+
+### Build API image
+
+```bash
+docker build -t viktorbarzin/realestatecrawler:latest crawler/
+```
+
+### Build Frontend image
+
+```bash
+docker build -t viktorbarzin/immoweb:latest crawler/frontend/
+```
+
+### Build both
+
+```bash
+docker build -t viktorbarzin/realestatecrawler:latest crawler/ && \
+docker build -t viktorbarzin/immoweb:latest crawler/frontend/
+```
+
+### Build with a specific tag (recommended for production)
+
+```bash
+# Use git commit SHA
+GIT_SHA=$(git rev-parse --short HEAD)
+docker build -t viktorbarzin/realestatecrawler:${GIT_SHA} -t viktorbarzin/realestatecrawler:latest crawler/
+docker build -t viktorbarzin/immoweb:${GIT_SHA} -t viktorbarzin/immoweb:latest crawler/frontend/
+```
+
+## Pushing Images
+
+### Login to Docker Hub (if not already)
+
+```bash
+docker login -u viktorbarzin
+```
+
+### Push API image
+
+```bash
+docker push viktorbarzin/realestatecrawler:latest
+```
+
+### Push Frontend image
+
+```bash
+docker push viktorbarzin/immoweb:latest
+```
+
+### Push with specific tag
+
+```bash
+GIT_SHA=$(git rev-parse --short HEAD)
+docker push viktorbarzin/realestatecrawler:${GIT_SHA}
+docker push viktorbarzin/realestatecrawler:latest
+docker push viktorbarzin/immoweb:${GIT_SHA}
+docker push viktorbarzin/immoweb:latest
+```
+
+## Build and Push Everything (Full Release)
+
+```bash
+GIT_SHA=$(git rev-parse --short HEAD)
+
+# Build
+docker build -t viktorbarzin/realestatecrawler:${GIT_SHA} -t viktorbarzin/realestatecrawler:latest crawler/
+docker build -t viktorbarzin/immoweb:${GIT_SHA} -t viktorbarzin/immoweb:latest crawler/frontend/
+
+# Push
+docker push viktorbarzin/realestatecrawler:${GIT_SHA}
+docker push viktorbarzin/realestatecrawler:latest
+docker push viktorbarzin/immoweb:${GIT_SHA}
+docker push viktorbarzin/immoweb:latest
+```
+
+## CI/CD Note
+
+Drone CI automatically builds and pushes images on push to `master` (see `.drone.yml`).
+The manual process above is for when you need to build/push outside of CI, such as:
+- Hotfix deployments
+- Testing image builds locally before pushing
+- Deploying from a non-master branch
+
+## Notes
+
+- The API Dockerfile installs system deps (OpenCV, Tesseract, MariaDB client) and Python deps via Poetry
+- The Frontend Dockerfile is a multi-stage build: Node builder -> Nginx runtime
+- Always tag with both `:latest` and a specific tag (git SHA or version) for traceability
+- Use `docker buildx` for cross-platform builds if deploying to ARM nodes