Publish preinstallable plugin release artifact for Ouroboros packages

[den-sq]

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.

[den-sq]

Feeds the Ouroboros production package flavor matrix:

• Build core-only, plugins CPU, and plugins CUDA production package flavors ouroboros#87
• Support bundled preinstalled plugins in production packages ouroboros#89

This should produce the stable neuroglancer plugin artifact that the package-flavor workflow can preinstall.

[tavateva]

Time Estimate: 2-3 hours

Breakdown:

• Release workflow setup: ~1h
• Artifact packaging (frontend bundle + metadata): ~0.5h
• Verification (artifact install into Ouroboros): ~1h
• Documentation: ~0.5h

Complexity factors:

• Neuroglancer plugin is frontend-only (no backend Docker image)
• Simpler than autoseg plugin artifacts (no CPU/CUDA variants)
• Must match Ouroboros plugin folder layout expectations

Dependencies:

• No blocking dependencies
• Can be developed/tested independently

[den-sq]

Closed by #5, #7, #8.