feat: Phase 3 — web dashboard, testing, and CI/CD

- Remove multi-marketplace from Phase 3
- Add FastAPI web UI on port 8766 with basic auth
- Add 6 Jinja2 templates (dashboard, keywords, users, ads, stats)
- Add pytest test suite (45 tests, 49% coverage)
- Add GitHub Actions CI/CD workflow
- Update docker-compose.yml to expose web UI port
- Update Dockerfile to include tests

.github/workflows/ci.yml

@@ -0,0 +1,38 @@
+name: CI
+
+on:
+  push:
+    branches: [main, "feat/*"]
+  pull_request:
+    branches: [main]
+
+jobs:
+  lint-and-test:
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: worker
+
+    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 -r requirements.txt
+          pip install pytest pytest-asyncio pytest-cov flake8
+
+      - name: Lint with flake8
+        run: |
+          flake8 src/ --count --show-source --statistics \
+            --max-line-length 120 \
+            --ignore=E501,W503
+
+      - name: Test with pytest
+        run: |
+          PYTHONPATH=src pytest --cov=notifier --cov=scraper --cov=db --cov=health --cov-report=term-missing --cov-fail-under=49 tests/