fix(ci): install pytestarch in backend tests job (#177)

CI was missing pytestarch dependency, causing test_architecture.py to fail
at collection time. Switch to requirements-test.txt which includes all
test dependencies.

https://claude.ai/code/session_01GaxovK2uVyVxUtXde9hU4P

.github/workflows/ci.yml

@@ -29,7 +29,7 @@ jobs:
         with:
           python-version: "3.12"
           cache: pip
-          cache-dependency-path: document-parser/requirements.txt
+          cache-dependency-path: document-parser/requirements-test.txt
 
       - name: Install system dependencies
         run: sudo apt-get update && sudo apt-get install -y --no-install-recommends poppler-utils
@@ -37,8 +37,8 @@ jobs:
       - name: Install Python dependencies
         run: |
           pip install --upgrade pip
-          pip install -r requirements.txt
-          pip install pytest pytest-asyncio httpx ruff
+          pip install -r requirements-test.txt
+          pip install httpx ruff
 
       - name: Lint
         run: ruff check .