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>

vitest.config.mts

@@ -0,0 +1,24 @@
+import { defineConfig } from 'vitest/config';
+
+export default defineConfig({
+  define: {
+    'process.env.NODE_ENV': '"test"',
+  },
+  test: {
+    globals: true,
+    environment: 'jsdom',
+    setupFiles: ['./vitest.setup.ts'],
+    exclude: ['e2e/**', 'node_modules/**'],
+    coverage: {
+      provider: 'v8',
+      include: ['src/**/*.{ts,tsx}'],
+      exclude: ['src/**/*.test.{ts,tsx}', 'src/test-utils.tsx', 'src/index.tsx'],
+      thresholds: {
+        lines: 80,
+        functions: 80,
+        branches: 80,
+        statements: 80,
+      },
+    },
+  },
+});