feat: scaffold headlamp-argocd-plugin with standard plugin structure

Adds the full plugin scaffold matching the Headlamp plugin pattern
(polaris, kube-vip, etc.):
- package.json with full devDependencies (Vitest, TypeScript, ESLint, Prettier)
- tsconfig.json, vitest.config.mts, vitest.setup.ts
- src/index.tsx with ArgoCDErrorBoundary and stub Applications route
- src/index.test.tsx smoke test to verify module importability
- CLAUDE.md documentation for future development
- .gitignore for node_modules/dist
- pnpm-lock.yaml pinned via packageManager field

ArtifactHub metadata already present (created by Hugh in PRI-186).

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

src/index.test.tsx

@@ -0,0 +1,16 @@
+import React from 'react';
+import { describe, it, expect } from 'vitest';
+import { render } from '@testing-library/react';
+import '@testing-library/jest-dom';
+
+/**
+ * Minimal test to verify the plugin index module loads without throwing.
+ * Full component tests will be added in subsequent tasks.
+ */
+describe('ArgoCD Plugin Scaffold', () => {
+  it('index module is importable', async () => {
+    // Dynamic import to verify the module parses and exports correctly
+    const mod = await import('./index');
+    expect(mod).toBeDefined();
+  });
+});