feat: add full URL support for custom Polaris dashboards

- Add isFullUrl() helper to detect full vs proxy URLs
- Support both K8s proxy URLs and direct HTTP/HTTPS URLs
- Use fetch() for full URLs, ApiProxy for K8s proxy URLs
- Improve error messages with context-specific guidance
- Update settings with examples for both URL types
- Version bump to 0.2.3

Generated with [Claude Code](https://claude.ai/code)
via [Happy](https://happy.engineering)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "headlamp-polaris-plugin",
-  "version": "0.2.2",
+  "version": "0.2.3",
   "description": "Headlamp plugin for Fairwinds Polaris audit results",
   "scripts": {
     "start": "headlamp-plugin start",