Finalize Neuroglancer production packaging release

[den-sq]

Summary

Finalizes Neuroglancer plugin production packaging release metadata.

• Documents the production pin as v1.0.0 with the legacy release.zip asset.
• Sets package metadata to version 1.0.0.
• Adds release manifest metadata for future named artifacts.
• Adds npm run validate:release and runs it in the release workflow.

Closes #6.

Validation

• Fix-to-staging PR Finalize Neuroglancer production packaging metadata #7 passed.
• Staging smoke tag: v1.0.0-packaging-smoke.6
• Build and Release Plugin run passed: https://github.com/ChengLabResearch/neuroglancer-plugin/actions/runs/28620206300

[tavateva]

✅ READY

Issue coverage: Closes #6 (Finalize production packaging release).

What's here:

• CI workflow gets a PR trigger + upload-artifact step, so the build runs on every relevant PR change rather than only on tags; the Upload Release step is correctly gated on startsWith(github.ref, 'refs/tags/').
• Job renamed plugin-artifact; actions bumped to v4; artifact named neuroglancer-plugin-<tag>.zip (replaces the legacy bare release.zip).
• build:release runs write-release-manifest.mjs to emit plugin-release.json; validate:release immediately asserts all required manifest fields match package.json and env — good.
• package.json version bumped to 1.0.0.
• README fixes the install URL (We-Gold → ChengLabResearch) and documents both the legacy v1.0.0 / release.zip pin (which Ouroboros #95 records as the production pin) and the new named-artifact format for future releases.

CI: plugin-artifact — ✅ pass (both runs).

No issues found.