feat: add image preview with drag-and-drop support

- Add ImagePreview component for displaying embedded image thumbnails
- Enable drag-and-drop functionality for images in FloatingPromptInput
- Configure Tauri asset protocol to properly serve local image files
- Support image mentions via @path syntax in prompts
- Add visual feedback for drag hover states
- Implement full-size image preview dialog with navigation
- Handle duplicate images and limit preview to 10 thumbnails

src-tauri/tauri.conf.json

@@ -18,7 +18,11 @@
       }
     ],
     "security": {
-      "csp": null
+      "csp": "default-src 'self'; img-src 'self' asset: https://asset.localhost blob: data:; style-src 'self' 'unsafe-inline'; script-src 'self' 'unsafe-eval'",
+      "assetProtocol": {
+        "enable": true,
+        "scope": ["**"]
+      }
     }
   },
   "plugins": {