[docs]: Migrate docs to Sveltekit

[BeeMargarida]

Description

Related to https://github.com/svelteuidev/svelteui/issues/324.

Migration of the docs to SK. Fixes a lot of bugs, including the broken dark theme.

Before submitting the PR, please make sure you do the following

• [x] Read the Contributing guide
• [x] Prefix your PR title with [@svelteui/core], [@svelteui/actions], [@svelteui/motion], [@svelteui/core], [core], or [docs].
• [x] Include a description of the changes made in the PR description and in the commit messages.
• [ ] Include screenshots/videos of the changes made.
• [x] Verify that the linter and tests are passing, with yarn lint and yarn test or just run yarn prepush.

[BeeMargarida]

Missing a rebase with main + double checking that everything is alright. It will be done this week. This is blocking a new release.