refactor: adopt svelte 5 for subsequent development

[ACTCD]

Since Svelte 5 Release Candidate phase have arrived, and the ongoing UI refactoring involves a lot of Svelte code refactoring, we decided to adopt Svelte 5 preview in advance for subsequent development work.

There are no obvious issues in the current version build test, except for a few svelte/transition related errors. We just need to wait for the official resolution of related issues.