feat: migrate to pyproject.toml, add test suites, split CI workflows

- Replace requirements.txt with pyproject.toml for modern Python packaging
- Add unit, integration, lint and security test suites under tests/
- Add utils/export_runtime_requirements.py and utils/check_hadolint_sarif.py
- Split monolithic CI into reusable lint.yml, security.yml and tests.yml
- Refactor ci.yml to orchestrate reusable workflows; publish on semver tag only
- Modernize Dockerfile: pin python:3.12-slim, install via pyproject.toml
- Expand Makefile with lint, security, test and CI targets
- Add test-e2e via act with portfolio container stop/start around run
- Fix navbar_logo_visibility.spec.js: win.fullscreen() → win.enterFullscreen()
- Set use_reloader=False in app.run() to prevent double-start in CI
- Add app/core.* and build artifacts to .gitignore
- Fix apt-get → sudo apt-get in tests.yml e2e job
- Fix pip install --ignore-installed to handle stale act cache

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/unit/test_compute_card_classes.py

@@ -0,0 +1,39 @@
+import unittest
+
+from app.utils.compute_card_classes import compute_card_classes
+
+
+class TestComputeCardClasses(unittest.TestCase):
+    def test_single_card_uses_full_width_classes(self):
+        lg_classes, md_classes = compute_card_classes([{"title": "One"}])
+
+        self.assertEqual(lg_classes, ["col-lg-12"])
+        self.assertEqual(md_classes, ["col-md-12"])
+
+    def test_two_cards_split_evenly(self):
+        lg_classes, md_classes = compute_card_classes([{}, {}])
+
+        self.assertEqual(lg_classes, ["col-lg-6", "col-lg-6"])
+        self.assertEqual(md_classes, ["col-md-6", "col-md-6"])
+
+    def test_three_cards_use_thirds(self):
+        lg_classes, md_classes = compute_card_classes([{}, {}, {}])
+
+        self.assertEqual(lg_classes, ["col-lg-4", "col-lg-4", "col-lg-4"])
+        self.assertEqual(md_classes, ["col-md-6", "col-md-6", "col-md-12"])
+
+    def test_five_cards_use_balanced_large_layout(self):
+        lg_classes, md_classes = compute_card_classes([{}, {}, {}, {}, {}])
+
+        self.assertEqual(
+            lg_classes,
+            ["col-lg-6", "col-lg-6", "col-lg-4", "col-lg-4", "col-lg-4"],
+        )
+        self.assertEqual(
+            md_classes,
+            ["col-md-6", "col-md-6", "col-md-6", "col-md-6", "col-md-12"],
+        )
+
+
+if __name__ == "__main__":
+    unittest.main()