feat(web): render page icon emoji in sidebar sub-items

Show the per-page icon (emoji from page manifest metadata.icon)
in collapsible plugin page sub-items.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

web/src/app/home/components/home-sidebar/HomeSidebar.tsx

@@ -1142,6 +1142,7 @@ function PluginPagesNav() {
                                 onClick={() => navigate(route)}
                                 className="select-none"
                               >
+                                {page.icon && <span>{page.icon}</span>}
                                 <span>{page.name}</span>
                               </SidebarMenuSubButton>
                             </SidebarMenuSubItem>