refactor: rename npm package to headlamp-polaris-plugin

Aligns npm package name with the repo and ArtifactHub package name.
Updates all references: package.json, registerPluginSettings, Dockerfile,
release workflow tarball URLs, artifacthub-pkg.yml archive-url, and README.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

package.json

@@ -1,5 +1,5 @@
 {
-  "name": "polaris-headlamp-plugin",
+  "name": "headlamp-polaris-plugin",
   "version": "0.0.8",
   "description": "Headlamp plugin for Fairwinds Polaris audit results",
   "scripts": {