Update vulnerable Svelte build toolchain

[PathGao]

Fixes #309

Updates SvelteKit, Svelte, Vite, and the matching adapter/plugin/check packages within their existing major release lines. The lockfile refresh also updates affected transitive packages.

Pins cookie to 0.7.2 because the latest SvelteKit 2 dependency range still resolves its vulnerable 0.6.0 release.

The complete resolved lockfile is clean under npm audit.

This is the next stacked change after #308; merge the already-listed predecessor PRs first, then this PR.

Validated with npm ci, npm run check (0 errors; one Settings drag-header accessibility warning detected by the newer checker is being handled separately), npm test (136 passing), npm run build, npm audit (0 vulnerabilities), and cargo test (21 passing).

[PathGao]

@alecdotdev This is the next stacked PR after #308. It updates the Svelte build toolchain and makes the full resolved lockfile clean under npm audit; please review it after the predecessor chain has merged. I also found one accessibility warning exposed by the newer checker and will send that as a separate focused follow-up.