chore: add linting, formatting, and type-checking

Add ESLint, Prettier, and TypeScript config files extending the shared
Headlamp plugin configs. Add npm scripts for lint/format. Auto-fix
existing source files. Add CI workflow for PRs and main pushes.

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

src/index.tsx

@@ -1,7 +1,4 @@
-import {
-  registerRoute,
-  registerSidebarEntry,
-} from '@kinvolk/headlamp-plugin/lib';
+import { registerRoute, registerSidebarEntry } from '@kinvolk/headlamp-plugin/lib';
 import React from 'react';
 import PolarisView from './components/PolarisView';