Activate plugin namespace drive-letter regression

The current upstream js/bun/plugin/plugin-namespace-drive-letter.test.ts is still replaced with a synthetic TODO even though Home’s real module loader now appears to carry the resolver guard.

The regression registers one-letter plugin namespaces (c and C) and imports a missing absolute Windows drive path. The module loader must treat C: as a drive prefix, reach filesystem resolution, and reject the import instead of dispatching it to the plugin namespace.

Acceptance criteria:

• execute the unmodified upstream fixture instead of a TODO
• run the nested Home process with its preload plugin
• reject the missing drive path without producing the plugin module
• pass the exact fixture (1/1) and complete home_test gate

Continues #66 and #81 after #91.

Completed and pushed to main in 2c244cf (feat(test): activate plugin drive namespace regression).

The unmodified current Bun fixture now runs through Home’s native corpus runner and a nested Home process with a preload plugin. The missing C:\\... path is rejected through filesystem resolution instead of being captured by the registered one-letter C plugin namespace.

Verification:

• exact upstream fixture: 1 passed, 0 failed, 0 unsupported, 0 todo
• debug build: passed
• Zig formatting and diff checks: passed
• complete home_test gate: passed with zero failures

Commit author and committer are Chris chrisbreuer93@gmail.com; no coauthors.