Add Lucide icon picker to the definition edit sheet

Ship a curated 36-glyph household subset via named lucide-react imports
(bundled, no CDN), offer it as a grid picker in the edit sheet, send the
chosen icon in create and edit bodies, and render it on the list row
with a generic fallback for no icon or an unknown legacy value.

Task b50b048f-40f6-418e-b571-ef6be3796296

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

admin/package.json

@@ -10,6 +10,7 @@
     "test": "vitest run"
   },
   "dependencies": {
+    "lucide-react": "^1.47.0",
     "react": "^19.2.0",
     "react-dom": "^19.2.0"
   },
@@ -24,4 +25,4 @@
     "vite": "^7.1.5",
     "vitest": "^3.2.4"
   }
-}
+}