Publish preinstallable plugin release artifact for Ouroboros packages #4

Goal

Publish a stable neuroglancer plugin release artifact suitable for bundling into Ouroboros production packages.

Context

The Ouroboros production release plan includes two plugin bundles:

• core + neuroglancer plugin + autoseg CPU
• core + neuroglancer plugin + autoseg CUDA

Ouroboros will need to fetch or stage a versioned neuroglancer plugin artifact during release packaging.

Scope

• Ensure the release artifact contains the plugin package.json, frontend bundle, icon, and any runtime assets needed by Ouroboros.
• Ensure the artifact layout matches what Ouroboros plugin installation expects.
• Add or confirm a release workflow that uploads the built plugin artifact on version tags.
• Document the artifact name and expected install/preinstall path.
• Include enough version metadata for Ouroboros to install idempotently.

Acceptance Criteria

• A tagged release produces a downloadable plugin artifact.
• The artifact can be unpacked into Ouroboros' plugin folder and detected by the app.
• The artifact can be used by the future Ouroboros package-flavor workflow without rebuilding the plugin.