Upstream bump: svelte 5.56.8 / kit 2.70.2

[github-actions]

Sync work order (Loop 1 — see LOOPS.md)

upstream	pinned	latest
svelte	5.56.3	5.56.8
@sveltejs/kit	2.64.0	2.70.2

Steps

1. Bump the pins: examples/playground/package.json (exact), peer ranges in packages/core and packages/kit, and the pin table in VERSIONING.md.
2. pnpm install && pnpm test && pnpm --filter syn-playground build
3. Run the playground click matrix (see TESTING.md layer 4) — classic, mixed, runes, React island.
4. Open a PR titled chore: sync svelte 5.56.8 / kit 2.70.2 including the suite output. Changeset: patch.

Opened automatically by upstream-watch. Gate: CI + human merge.