Replace emoji-as-icons in editor chrome with Font Awesome

Unicode emoji/glyphs (Sitesmith's sparkle, lock, close X) render as
tofu on systems without an emoji font. Swap for the FA4 glyphs the
rest of the chrome already uses:
- SitesmithButton/SitesmithModal: sparkle -> fa-magic, lock -> fa-lock
- ContextMenu "Ask Sitesmith" entry: sparkle -> fa-magic (via new
  optional MenuItem.icon field)
- TemplateModal/SitesmithModal close buttons, PagesPanel delete,
  AssetsPanel delete/cancel: ✕ -> fa-times / fa-trash

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

craft/src/panels/left/AssetsPanel.tsx

@@ -296,7 +296,7 @@ export const AssetsPanel: React.FC = () => {
                     cursor: 'pointer',
                   }}
                 >
-                  ✕
+                  <i className="fa fa-times" aria-hidden />
                 </button>
               </div>
             ) : (
@@ -328,7 +328,7 @@ export const AssetsPanel: React.FC = () => {
                 onMouseEnter={(e) => { (e.target as HTMLElement).style.opacity = '1'; }}
                 onMouseLeave={(e) => { (e.target as HTMLElement).style.opacity = '0.7'; }}
               >
-                &#10005;
+                <i className="fa fa-times" aria-hidden />
               </button>
             )}
           </div>

craft/src/panels/left/PagesPanel.tsx

@@ -394,7 +394,7 @@ export const PagesPanel: React.FC = () => {
                       cursor: 'pointer',
                     }}
                   >
-                    ✕
+                    <i className="fa fa-trash" />
                   </button>
                 )}
               </div>