fix: generate route types only once during svelte-kit sync

[svelte-triage-bot]

• Resolving Vite's build config already runs the compile plugin's sync.all; the CLI then redundantly rebuilds the manifest and generates types.
• Preserve Vite-based configuration (#15944) and compile-time generation of real build artifacts (#16813, #16885). Skip the CLI's explicit pass when the applied compile plugin is present.
• Retain the types-only fallback for plugin-free or filtered-plugin configs rather than deleting all_types or switching to serve-mode resolution, which would change configuration semantics.
• Apply the same guard to the repository's sync-all script; cover single-pass generation, fresh custom roots/output directories, fallback configurations, retained build artifacts, and environment --mode handling.

Fixes #17394

[pkg-svelte-dev]

Install the latest version of @sveltejs/kit from d5dbaf5:

pnpm add https://pkg.svelte.dev/@sveltejs/kit/c/d5dbaf59b177ff5a5b5a3312132dfa39d1d86a4b

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/kit/pr/17395

Note

This PR is from a fork. A maintainer must approve approve each commit before it can be built and installed.

[changeset-bot]

🦋 Changeset detected

Latest commit: d5dbaf5

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@sveltejs/kit	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR