Relax Playwright dependency for Nix, pin exact version in Docker

- Allow playwright>=1.46.0,<2 in pyproject.toml for Nix compatibility
- Add pip constraints.txt to pin playwright==1.46.0 in container builds
- Enforce constraints during Docker image build

https://chatgpt.com/share/694b0180-2734-800f-830e-44e15d0a527d

Dockerfile

@@ -13,8 +13,9 @@ WORKDIR /app
 
 # Option B: build from source (current repo)
 COPY pyproject.toml README.md LICENSE /app/
+COPY constraints.txt /app/
 COPY src /app/src
-RUN pip install --no-cache-dir .
+RUN pip install --no-cache-dir -c /app/constraints.txt .
 
 # Default entrypoint: environment-driven bootstrap
 ENTRYPOINT ["matomo-bootstrap"]