Upgrade to Svelte 5

[eyeseast]

Svelte 5 is supposed to be compatible with Svelte 4, so this should just mean changing the version number in package.json, though I expect we'll run into some dependency issues.

https://svelte.dev/docs/svelte/v5-migration-guide

Migrating components to use the new runes syntax will be a longer process that we can do incrementally, though I suspect it'll ultimately make the code better. We might make a dedicated milestone for migration.

[eyeseast]

This is currently blocked by a couple dependencies that need to be upgraded:

• addon-svelte-csf
• svelte-select

We should do the storybook upgrade first (#492), as well as any other upgrades that may have breaking changes.

• Vite
• Sentry

Finally, we should do another dependency audit and remove anything we're not using.

[eyeseast]

We could replace svelte-select with svelecte, if we needed. Looks like it might be more maintained.