Add a Font Awesome icon gallery to the properties panel, draggable onto the screen

New "Icône" widget (<i class="...">, color/size customizable exactly like any other widget) plus a curated set of ~250 verified Font Awesome 5 Free solid icon names (fontawesome_icons.py) — not the full ~1500-icon catalog, since an embedded list needs to be guaranteed accurate (a wrong class name silently renders as a blank glyph); any other valid FA5 class still works by typing it directly into the widget's "Icône" setting.

The gallery lives in the (now always-visible) top of the right floating panel, searchable, with each tile both clickable and HTML5-draggable onto the canvas — either action posts to element_add with the chosen icon_class, which now seeds the new element's class instead of leaving it on the generic default. Available in the element-type template editor too, since it reuses screen_edit.html.

Loads Font Awesome 5.15.4 (cdnjs) alongside the existing animate.css/Bulma links, in both the editor and /play.

Verified end to end: gallery renders with real icon glyphs, clicking/simulated-drop creates a correctly-classed <i> element, and the actual /play route renders it with Font Awesome loaded. Full suite green (89).

templates/play.html

@@ -8,6 +8,7 @@
 <link rel="stylesheet" href="{{ google_fonts_link }}">
 <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/animate.css/4.1.1/animate.min.css">
 <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bulma@1.0.2/css/bulma.min.css">
+<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/5.15.4/css/all.min.css">
 <style>
   body{ margin:0; background:#000; }
   /* ---------- Zone de jeu à proportion fixe (voir #playFrame) ----------