Reskin the whole admin UI (not just game widgets) with Bulma

Loads Bulma 1.0.2 in base.html (data-theme="dark" for its native dark palette) for every page that extends it, plus play.html directly. Converts every admin template — index, game dashboard, screens list, element types, object new/edit, data form/list — to real Bulma markup: navbar, breadcrumb component, box/card, field/control/input/select, table, notification, buttons, and a native Bulma modal for the data-row detail popup. Forge's own style.css keeps only what Bulma doesn't cover (the fixed-viewport builder/object-edit layouts, the element tree, canvas, flow-graph editor) and now acts as a secondary/override layer rather than a competing design system, matching how per-element inline customization already overrides widget defaults.

screen_edit.html (the 3-panel screen builder) gets the same navbar/breadcrumb/button treatment plus its top rename form, but its flow-graph node editor, canvas and element tree keep their existing custom styling — several of their inputs have JS relying on exact DOM sibling structure (e.g. slider oninput reading nextElementSibling) or Bulma's own select/wrapper requirement, and reskinning them without a browser to verify against risked silently breaking the app's most complex feature. Buttons and headings there are still fully converted (safe, purely additive class changes).

Verified: full test suite green, every route smoke-rendered 200 OK via the test client after the change.

templates/base.html

@@ -1,17 +1,27 @@
 <!DOCTYPE html>
-<html lang="fr">
+<html lang="fr" data-theme="dark">
 <head>
 <meta charset="UTF-8">
 <meta name="viewport" content="width=device-width, initial-scale=1.0">
 <title>{% block title %}Forge Engine{% endblock %}</title>
+<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bulma@1.0.2/css/bulma.min.css">
 <link rel="stylesheet" href="{{ url_for('static', filename='style.css') }}">
 {% block extra_head %}{% endblock %}
 </head>
 <body class="{% block body_class %}{% endblock %}">
-<header class="topbar">
-  <a href="{{ url_for('index') }}" class="brand">🛠️ Forge Engine</a>
-  {% block breadcrumb %}{% endblock %}
-</header>
+<nav class="navbar topbar" role="navigation" aria-label="main navigation">
+  <div class="navbar-brand">
+    <a href="{{ url_for('index') }}" class="navbar-item brand"><strong>🛠️ Forge Engine</strong></a>
+  </div>
+</nav>
+{% block breadcrumb_wrap %}
+<nav class="breadcrumb breadcrumbBar" aria-label="breadcrumbs">
+  <ul>
+    <li><a href="{{ url_for('index') }}">🛠️ Mes jeux</a></li>
+    {% block breadcrumb %}{% endblock %}
+  </ul>
+</nav>
+{% endblock %}
 <main class="content {% block content_class %}{% endblock %}">
   {% block content %}{% endblock %}
 </main>