fix(vite): load server pages unpicked in server environments

[brenelz]

Fixes #16.

With serverComponents: true, the SSR environment loaded each server page twice. The manifest imported it as ?pick=default, and @solidjs/vite-plugin's server-function handler imported the plain file. Both instances called registerServerReference with the same id, and the second call replaced the first. The GET grant that @solidjs/router's query() makes was bound to the replaced function, so every client-side call to a server page returned 405.

In server-consumer environments, the Vite adapter now uses the plain id for every ref to a server page's file ($component, $$route, and any handler refs), in both the virtual module and the build inputs. The handler already loads that file whole, so a picked copy only added a second instance. Client environments still pick, so client bundles keep the stub and code splitting.

Verification:

• pnpm test passes (114 tests). The new test in test/vite.spec.ts checks that the ssr manifest imports the server page without ?pick=, and it fails without the change.
• I built a stories app (one server layout, two server pages, and a server action) against this branch's dist, with the local ?pick= workaround plugin removed. vite build now emits one registerServerReference per server page id instead of two. A Playwright run against the production server and vite dev navigated client-side to the server pages and submitted the form, and every /_server/data/... call returned 200. The same run against published 0.4.0 gets stuck on the first client navigation.

The third fix suggested in the issue, making a duplicate registerServerReference warn in @solidjs/web, is out of scope here.

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