Refactor: Image file resources

[WhiteMinds]

1. Replace the png files used in src/assets and other places with svg files as much as possible.
2. Replace loading.gif, loading_white.gif, blue_loading.gif in src/assets with CSS animation implementation.
3. Move all image files in src/assets to the folder of the code file that uses it.
   If it is used in two places, copy it once.
   If it is used three times or more, you can either copy it or consider building a common component for it.