Ship Android app by wrapping CRA build with Capacitor (#20)

Add Capacitor 7 scaffolding (config, android/, npm scripts, .env.mobile),
native back-button/safe-area chrome, icons/splash, and signing docs so
llm-fe ships one codebase to web and Android.

llm-fe/capacitor.config.ts

@@ -0,0 +1,27 @@
+import type { CapacitorConfig } from '@capacitor/cli';
+
+const config: CapacitorConfig = {
+  appId: 'com.aimloperations.chat',
+  appName: 'AI ML Chat',
+  webDir: 'build',
+  server: {
+    // Bundled assets; HashRouter (#24) handles deep links without a rewrite server.
+    androidScheme: 'https',
+  },
+  android: {
+    allowMixedContent: false,
+  },
+  plugins: {
+    SplashScreen: {
+      launchAutoHide: true,
+      backgroundColor: '#0f172a',
+      showSpinner: false,
+    },
+    Keyboard: {
+      // StatusBar does not overlay the WebView; keep resizeOnFullScreen for notch devices.
+      resizeOnFullScreen: true,
+    },
+  },
+};
+
+export default config;