chore: refactor

[eglitise]

This PR continues the preparation for migrating to Vite, and primarily changes many file locations:

• add a new assets directory in renderer, and move images, locales and stylesheets directories to it
• move main.js to main directory
• merge Root.jsx and routes.jsx (originally I only moved Root.jsx to its parent directory, but merging it with routes.jsx further improved clarity)
• add a new src directory in renderer and move all renderer contents to it, except HTML entrypoint files

Browser and Electron versions were tested to still work fine.

[jlipps]

seems good to me! we'll want to double check the CrowdIn integration works without issue after we merge.

[eglitise]

I think it should be fine, since the path for translation files was only defined in one file.