feat: add props system and refactor asset library architecture

messages/en/assetLibrary.json

@@ -3,12 +3,15 @@
   "button": "Assets",
   "characters": "Characters",
   "locations": "Locations",
+  "props": "Props",
   "noCharacters": "No characters",
   "noLocations": "No locations",
+  "noProps": "No props",
   "addCharacter": "Add Character",
   "addLocation": "Add Location",
+  "addProp": "Add Prop",
   "generateImage": "Generate Image",
   "regenerateImage": "Regenerate",
   "analyzeAssets": "Analyze Assets",
   "analyzing": "Analyzing..."
-}
+}