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>

.gitignore

@@ -0,0 +1,17 @@
+node_modules/
+dist/
+.pnp/
+.pnp.js
+*.log
+*.tgz
+.DS_Store
+.env
+.env.local
+coverage/
+.nyc_output/
+.cache/
+*.swp
+*.swo
+*~
+.vscode/
+.idea/