Fix build failure when prerendering dynamic routes

[77wisher77]

Summary

Change the /src/routes/+layout.ts prerender option from true to "auto".

Environment

• Arch Linux (7.1.5-arch1-1) / EndeavourOS
• Bun 1.3.14
• NodeJs 24.13.0
• SvelteKit 2.69.1
• Tauri CLI 2.11.4
• rustory branch/commit main/d1f086a14cede25408b6df30705f5a24c753d551

Problem

The root prerender = true setting is inherited by these dynamic routes:

• /vs-instances/[slug]
• /vs-instances/[slug]/edit
• /vs-mods/[slug]

These routes require parameterized destinations that are determined at runtime,
so SvelteKit cannot discover concrete paths during its prerender crawl.
Consequently, bun run tauri build --no-bundle fails with
handleUnseenRoutes errors.

I have attached a full, failed build log for inspection.

Solution

prerender = "auto" preserves prerendering for routes that can be discovered
while allowing the static SPA fallback to serve runtime parameter routes. SSR
remains disabled, so this matches the existing Tauri/adapter-static SPA
configuration without adding build-time data fetching or placeholder slugs.

Validation

• bun install --frozen-lockfile
• bun run check
• bun run lint
• bun run tauri build --no-bundle
• "Created" a local Vintage Story instance and viewed it in the list of instances
• Open a mod detail page from the mods list
• Installed a mod into an instance

References

• SvelteKit page options — prerender
• build-with-dynamic-routes-error.log