feat: add companion API and Android APK shell

apps/mobile/src/components/app-shell/AppShell.tsx

@@ -1,4 +1,5 @@
-import type { ReactNode } from 'react';
+import { useEffect, useState, type ReactNode } from 'react';
+import { useCompanion } from '../../api/CompanionContext.js';
 import type { ScreenId } from '../../app/navigation.js';
 import { BottomNav } from '../bottom-nav/BottomNav.js';
 
@@ -9,6 +10,26 @@ type AppShellProps = {
 };
 
 export function AppShell({ activeScreen, children, onNavigate }: AppShellProps) {
+  const { client } = useCompanion();
+  const [online, setOnline] = useState(false);
+
+  useEffect(() => {
+    let cancelled = false;
+
+    client
+      .health()
+      .then(() => {
+        if (!cancelled) setOnline(true);
+      })
+      .catch(() => {
+        if (!cancelled) setOnline(false);
+      });
+
+    return () => {
+      cancelled = true;
+    };
+  }, [client]);
+
   return (
     <div className="app-shell">
       <header className="app-header">
@@ -16,9 +37,9 @@ export function AppShell({ activeScreen, children, onNavigate }: AppShellProps)
           <p className="eyebrow">Hermes Mobile</p>
           <h1>Agent command center</h1>
         </div>
-        <div className="status-pill">
+        <div className={`status-pill ${online ? 'status-pill--online' : ''}`}>
           <span className="status-pill__dot" />
-          Companion pending
+          {online ? 'Online' : 'Offline'}
         </div>
       </header>
       <main className="app-main">{children}</main>