refactor: Upgrade to Vue 3 and Vuetify 3.

[Kelketek]

Upgrades the frontend to use Vue 3 alongside Vuetify 3 and Vuex 4.
Migrates the build system to Vite 5. This also resulted in several
small improvements such as:

1. Reduced payload by removing no-longer-needed workaround code for things Vuetify and Vue now natively support.

2. Also removed code for Credit card number validation/type determination on the frontend, which hasn't been needed since we moved to Stripe from Authorize.net.

3. Removes many, perhaps most, direct dependencies on the frontend.

4. Increases build speed significantly. Expected to increase even further once Vite replaces rollup.

5. Bifurcated the download button on Submissions so that you can choose to either use your browser's built-in viewer or else actually download the file to disk.

6. As an adjunct to 5, removed the 'zoom' feature for clicking on a submission, since our built-in zoom viewer never quite worked consistently, and the view button tends to create a better experience.

7. Removed 'floating action buttons'-- which aren't supported by our component framework anymore. These were primarily used on mobile to make those green buttons with a plus sign on them for adding stuff.

   People often didn't notice them anyway, for some reason, so now the button that appears on desktop appears on mobile, too, and those buttons are gone. Same with the blue editor toggle.

8. New content rating selector replaces old one to make it more obvious how it works and less easy to miss when fiddling with your settings.

9. Turned the upload revision form into a modal instead of just automatically creating a revision when the image is uploaded. You can also now submit a comment alongside the revision so you can do this in one go. It also makes it more obvious that you can (and should, when appropriate) mark the revision as the final.