fix: do not enable devtools from Vite's optional-peer-dep stub

[brenelz]

Problem

Any Start app that does not install @solidjs/start-devtools fails in dev on 3.0.0-next.31:

Uncaught SyntaxError: The requested module '/@id/__vite-optional-peer-dep:@solidjs/start-devtools:@solidjs/vite-plugin' does not provide an export named 'DevToolbar'

resolveDevtools falls back to resolving the package from the plugin's own file (for pnpm-isolated installs where devtools is only a dependency of the plugin). But @solidjs/start-devtools is declared an optional peer dependency of the plugin, so when it is absent Vite does not return null for that resolution — it returns its __vite-optional-peer-dep: stub (an empty module). The plugin took the stub as a real resolution, enabled the toolbar, and the generated client entry imported DevToolbar from an empty module.

Fix

Treat an id starting with __vite-optional-peer-dep: as "not installed" in both resolution attempts.

Verification

• Reproduced with the bare template + next.31 and no devtools installed; with the patched build the generated entry no longer imports devtools and the app boots with no console errors.
• examples/start-client/test/run.mjs: 45/45 (toolbar still wraps the app when devtools is installed).

🤖 Generated with Claude Code

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Latest commit: 4cdb3af

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

This PR includes changesets to release 1 package

Name	Type
@solidjs/vite-plugin	Patch

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