In a worker serve, imports into node_modules become
`/ns/m/node_modules/<pkg>?ns_worker=1`, but re-exports were left to
rewriteImports, which hands a package's own `export * from './sub'` to
the import map as a bare specifier. The import map routes that to the
deps-bundle shim, so the worker evaluated the whole bundle as well and
held a second copy of a package it had already loaded per module.

Worker imports and re-exports now both name the file Vite resolved, so
each module has one URL in the worker realm. The main realm is unchanged.

The vendorImportsAsHttp and processCodeForDevice comments still described
worker vendor imports as going through the deps-bundle bridge, and
transitive worker imports as unforkable; both predate ns_worker=1
propagation and contradict the per-module invariant this branch adds.