fix(navigation): unclip dropdowns and flip toward the side with more space

- Move <header> overflow:hidden into body.fullscreen scope and drop the
  implicit-vertical-clip overflow-x:auto from .navbar-nav so dropdown
  menus can escape the navbar.
- Drive top-level dropdowns through bootstrap.Dropdown (popperConfig
  strategy:'fixed'), and add a chooseDirection() helper that toggles
  .dropup/.dropdown on the .nav-item based on space above vs below
  before each show. Split the navigation.css rules to position the menu
  with top:100% or bottom:100% accordingly.
- Mark the dropdown toggle with data-bs-toggle="dropdown" in the
  template; cover that with a Jinja-rendered unit test and add Cypress
  specs for the header (opens downward) and footer (flips to .dropup)
  cases.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/unit/test_navigation_template.py

@@ -0,0 +1,70 @@
+import unittest
+from html.parser import HTMLParser
+from pathlib import Path
+
+from jinja2 import Environment, FileSystemLoader, select_autoescape
+
+
+class AnchorCollector(HTMLParser):
+    def __init__(self):
+        super().__init__()
+        self.anchors = []
+
+    def handle_starttag(self, tag, attrs):
+        if tag == "a":
+            self.anchors.append(dict(attrs))
+
+
+class TestNavigationTemplate(unittest.TestCase):
+    def test_top_level_dropdowns_have_bootstrap_toggle_attribute(self):
+        template_dir = Path(__file__).resolve().parents[2] / "app" / "templates"
+        environment = Environment(
+            loader=FileSystemLoader(template_dir),
+            autoescape=select_autoescape(),
+        )
+        environment.globals["url_for"] = lambda _endpoint, filename: (
+            f"/static/{filename}"
+        )
+
+        rendered = environment.get_template("moduls/navigation.html.j2").render(
+            menu_type="header",
+            platform={
+                "titel": "Portfolio",
+                "logo": {"cache": "logo.png"},
+            },
+            navigation={
+                "header": {
+                    "children": [
+                        {
+                            "name": "Apps",
+                            "description": "Application menu",
+                            "icon": {"class": "fa-solid fa-grid"},
+                            "children": [
+                                {
+                                    "name": "Example",
+                                    "description": "Example app",
+                                    "icon": {"class": "fa-solid fa-link"},
+                                    "url": "https://example.test",
+                                }
+                            ],
+                        }
+                    ]
+                }
+            },
+        )
+
+        parser = AnchorCollector()
+        parser.feed(rendered)
+        dropdown_toggles = [
+            anchor
+            for anchor in parser.anchors
+            if "nav-link" in anchor.get("class", "")
+            and "dropdown-toggle" in anchor.get("class", "")
+        ]
+
+        self.assertEqual(len(dropdown_toggles), 1)
+        self.assertEqual(dropdown_toggles[0].get("data-bs-toggle"), "dropdown")
+
+
+if __name__ == "__main__":
+    unittest.main()