chore: bump lib-core.panel dep to 0.4.0

Engine resolver does exact strcmp on dep versions, so consumer manifests
must pin the new lib-core.panel 0.4.0 to keep load-time resolution green.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

manifest.lib

@@ -5,7 +5,7 @@
     "api_min": "0.1",
     "deps": [
         {"id": "lib-core.inventory-list-display", "version": "0.1.1"},
-        {"id": "lib-core.panel", "version": "0.3.0"},
+        {"id": "lib-core.panel", "version": "0.4.0"},
         {"id": "lib-core.inventory-list", "version": "0.1.0"},
         {"id": "lib-core.composition", "version": "0.3.0"}
     ]