docs: add CI workflow and testing requirements documentation

- Add GitHub Actions CI pipeline with pytest, ruff, mypy
- Expand Tasks.md with implementation tracking and testing criteria
- Update CONTRIBUTING.md with CI requirements
- Add Testing-Requirements.md with coverage thresholds and PR checks

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

.github/workflows/ci.yml

@@ -0,0 +1,80 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  backend:
+    name: Backend Tests
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: backend
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install -e ".[dev]"
+
+      - name: Run tests with coverage
+        run: pytest --cov=app --cov-report=term-missing --cov-fail-under=80
+
+      - name: Upload coverage report
+        uses: actions/upload-artifact@v4
+        with:
+          name: coverage-report
+          path: backend/htmlcov/
+          retention-days: 7
+
+  ruff:
+    name: Lint
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: backend
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+
+      - name: Install dependencies
+        run: pip install ruff
+
+      - name: Run ruff
+        run: ruff check .
+
+  mypy:
+    name: Type Check
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: backend
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+
+      - name: Install dependencies
+        run: pip install -e ".[dev]"
+
+      - name: Run mypy
+        run: mypy app