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>

app/utils/compute_card_classes.py

@@ -32,7 +32,7 @@ def compute_card_classes(cards):
                     lg_classes.append("col-lg-6")
                 else:
                     lg_classes.append("col-lg-4")
-    # md classes: If the number of cards is even or if not the last card, otherwise "col-md-12"
+    # Use a full-width last card on medium screens only when the total count is odd.
     md_classes = []
     for i in range(num_cards):
         if num_cards % 2 == 0 or i < num_cards - 1: