fix: use linux.desktop.entry for custom desktop Icon field

electron-builder v26 rejects arbitrary keys in linux.desktop — the
correct schema wraps custom .desktop overrides inside desktop.entry.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/ui/package.json

@@ -267,8 +267,10 @@
       "description": "An autonomous AI development studio that helps you build software faster using AI-powered agents",
       "synopsis": "AI-powered autonomous development studio",
       "desktop": {
+        "entry": {
           "Icon": "/opt/Automaker/resources/logo_larger.png"
         }
+      }
     },
     "rpm": {
       "depends": [