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>

CLAUDE.md

@@ -0,0 +1,64 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project
+
+Headlamp plugin for ArgoCD visibility. Monitors ArgoCD Applications, Rollouts, and health status via the ArgoCD REST API proxied through Kubernetes. Read-only — no cluster write operations.
+
+- **Plugin name**: `argocd`
+- **Target**: Headlamp >= v0.26
+- **Data source**: ArgoCD server at `/api/v1/namespaces/argocd/services/argocd-server/proxy/api/v1/applications`
+- **RBAC**: `get`/`list` on `services/proxy` for `argocd-server` in `argocd` namespace
+
+## Commands
+
+```bash
+pnpm start          # dev server with hot reload
+pnpm build          # production build
+pnpm package        # package for headlamp
+pnpm tsc            # TypeScript type check (no emit)
+pnpm lint           # ESLint
+pnpm lint:fix       # ESLint with auto-fix
+pnpm format         # Prettier write
+pnpm format:check   # Prettier check
+pnpm test           # vitest run
+pnpm test:watch     # vitest watch mode
+```
+
+All tests and `pnpm tsc` must pass before committing.
+
+## Architecture
+
+```
+src/
+├── index.tsx               # Plugin entry: registerRoute, registerSidebarEntry; ArgoCDErrorBoundary
+├── test-utils.tsx          # Shared test fixtures
+├── api/
+│   └── argocd.ts           # ArgoCD API types, ApiProxy request helpers
+└── components/
+    └── ArgoCDStubView.tsx  # Placeholder Applications List view
+```
+
+## Code conventions
+
+- Functional React components only — class components only for error boundaries (ArgoCDErrorBoundary in index.tsx)
+- All imports from `@kinvolk/headlamp-plugin/lib` and `@kinvolk/headlamp-plugin/lib/CommonComponents`
+- `@mui/material` is available as a shared external via Headlamp — use `useTheme` from `@mui/material/styles` for theming. Do NOT add `@mui/material` to package.json dependencies.
+- Use `useTheme()` + `theme.palette.*` for all theme-aware colors — never use `var(--mui-palette-*)` CSS variables
+- No other UI libraries (no Ant Design, etc.)
+- TypeScript strict mode — no `any`, use `unknown` + type guards at API boundaries
+- Context provider wraps each route component in `index.tsx`
+- All registered components wrapped in `ArgoCDErrorBoundary` for graceful error handling
+- Tests: vitest + @testing-library/react, mock with `vi.mock('@kinvolk/headlamp-plugin/lib', ...)`
+- `vitest.setup.ts` provides a spec-compliant `localStorage` shim for Node 22+ compatibility
+
+## Testing
+
+Mock pattern for headlamp APIs:
+```typescript
+vi.mock('@kinvolk/headlamp-plugin/lib', () => ({
+  ApiProxy: { request: vi.fn().mockResolvedValue({}) },
+  K8s: { ResourceClasses: {} },
+}));
+```