feat(11-03): Alpine.js theme + i18n stores in base.html with top-right controls

- Add Alpine.store('theme') for Light/Dark/System cycling with localStorage persistence
- Add Alpine.store('i18n') with FR/EN translations for all static UI strings
- Add topbar with theme toggle button (:aria-label, @click cycle) and lang button
- Wrap main content in .main-wrapper + .topbar for layout structure
- Add .main-wrapper, .topbar, .topbar-controls styles to app.css
- Add test_theme_toggle_present integration test
- Fix test_dashboard_shows_recent_printers assertion (string now in i18n JS too)

tests/test_static.py

@@ -43,6 +43,16 @@ def test_packages_returns_200(client):
     assert response.status_code == 200
 
 
+
+def test_theme_toggle_present(client):
+    """GET / contains a theme toggle button (data-theme cycling control)."""
+    response = client.get("/")
+    assert response.status_code == 200
+    # The button's @click should reference $store.theme.cycle
+    assert "theme" in response.text
+    assert "cycle" in response.text or "store.theme" in response.text
+
+
 def test_dashboard_shows_recent_printers(client):
     """Dashboard renders names of recently-created printers from DB."""
     from imptune.db.models import Printer
@@ -62,7 +72,17 @@ def test_dashboard_shows_recent_printers(client):
     assert response.status_code == 200
     assert "TestPrinter-Alpha" in response.text
     assert "TestPrinter-Beta" in response.text
-    assert "No printers configured yet" not in response.text
+    # Use class-specific check: the string also appears in the i18n store JS
+    assert 'class="empty-state">No printers configured yet' not in response.text
+
+
+def test_theme_toggle_present(client):
+    """GET / contains a theme toggle button (data-theme cycling control)."""
+    response = client.get("/")
+    assert response.status_code == 200
+    # The button's @click should reference $store.theme.cycle
+    assert "theme" in response.text
+    assert "cycle" in response.text or "store.theme" in response.text
 
 
 def test_dashboard_shows_recent_packages(client):