feat(ApplicationsList): implement ArgoCD Applications List view

Implement the Applications List view for headlamp-argocd-plugin (PRI-189).

- Add src/components/ApplicationsList.tsx with table of all ArgoCD Applications
  showing: app name, namespace, project, health status, sync status,
  target revision, and last synced time
- Health/sync status badges using ArgoCD color conventions
- Filter controls: health dropdown, sync dropdown, project dropdown
- Friendly "ArgoCD not detected" error state when ArgoCD is unreachable
- Add src/api/argocd.ts with ArgoCD API types (Application, ApplicationsList)
- Add unit tests in src/__tests__/ApplicationsList.test.tsx:
  - Pure function tests for healthStatusToColor and syncStatusToColor
  - Filter logic unit tests
  - Component smoke tests (loading, error, data, empty states)
- Replace stub view in src/index.tsx with ApplicationsList component

Co-Authored-By: Paperclip <noreply@paperclip.ing>

src/index.tsx

@@ -7,6 +7,7 @@ import {
   StatusLabel,
 } from "@kinvolk/headlamp-plugin/lib/CommonComponents";
 import React from "react";
+import ApplicationsList from "./components/ApplicationsList";
 
 // --- Error boundary for plugin components ---
 
@@ -36,18 +37,6 @@ class ArgoCDErrorBoundary extends React.Component<
   }
 }
 
-// --- Stub Applications List View ---
-
-function ArgoCDStubView() {
-  return (
-    <SectionBox title="ArgoCD Applications">
-      <StatusLabel status="info">
-        Plugin scaffold — features coming soon.
-      </StatusLabel>
-    </SectionBox>
-  );
-}
-
 // --- Sidebar entry ---
 
 registerSidebarEntry({
@@ -75,7 +64,7 @@ registerRoute({
   exact: true,
   component: () => (
     <ArgoCDErrorBoundary>
-      <ArgoCDStubView />
+      <ApplicationsList />
     </ArgoCDErrorBoundary>
   ),
 });