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/package.json

@@ -3,6 +3,13 @@
   "version": "0.1.0",
   "private": true,
   "dependencies": {
+    "@capacitor/android": "^7.6.8",
+    "@capacitor/app": "^7.1.2",
+    "@capacitor/cli": "^7.6.8",
+    "@capacitor/core": "^7.6.8",
+    "@capacitor/keyboard": "^7.0.6",
+    "@capacitor/preferences": "^7.0.4",
+    "@capacitor/status-bar": "^7.0.6",
     "@emotion/cache": "^11.14.0",
     "@emotion/react": "^11.14.0",
     "@emotion/styled": "^11.14.0",
@@ -41,6 +48,10 @@
     "build": "NODE_ENV=production react-scripts build",
     "build:prod": "NODE_ENV=production react-scripts build && mkdir -p /var/www/prod.chat.aimloperations/html && cp -r ./build/* /var/www/prod.chat.aimloperations/html/",
     "build:beta": "bash -c 'set -a; source .env.beta; set +a; NODE_ENV=production react-scripts build' && mkdir -p /var/www/beta.chat.aimloperations/html && cp -r ./build/* /var/www/beta.chat.aimloperations/html/",
+    "build:mobile": "bash -c 'set -a; source .env.mobile; set +a; NODE_ENV=production react-scripts build' && npx cap sync android",
+    "android:open": "npx cap open android",
+    "android:sync": "npx cap sync android",
+    "assets:generate": "npx capacitor-assets generate --android",
     "test": "NODE_ENV=development react-scripts test",
     "test:ci": "CI=true NODE_ENV=development react-scripts test --watchAll=false --coverage=false",
     "eject": "react-scripts eject"
@@ -64,6 +75,7 @@
     ]
   },
   "devDependencies": {
+    "@capacitor/assets": "^3.0.5",
     "@types/bootstrap": "~5.2.10",
     "@types/lodash": "~4.17.13",
     "@types/react": "^18.3.16",