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/ANDROID.md

@@ -0,0 +1,117 @@
+# Android (Capacitor)
+
+Ship the CRA web build as an Android app via [Capacitor](https://capacitorjs.com/).
+One codebase: `llm-fe/` → web + Android WebView.
+
+Prerequisites for blockers already merged: JWT-only auth (#22), WebSocket lifecycle (#23), HashRouter (#24).
+
+## Prerequisites
+
+- **Node.js 20** (matches CI; Capacitor **7.x**)
+- **JDK 17+** (OpenJDK fine)
+- **Android Studio** (Ladybug+) with Android SDK Platform **35**, build-tools, and an emulator or device
+- Set `ANDROID_HOME` (or open the project once in Android Studio so `local.properties` is generated)
+
+## One-time / day-to-day
+
+```bash
+cd llm-fe
+npm ci
+npm run build:mobile   # loads .env.mobile → CRA build → cap sync android
+npm run android:open   # opens android/ in Android Studio
+```
+
+Or sync only after an existing `build/`:
+
+```bash
+npm run android:sync
+```
+
+## Environment
+
+| File | Purpose |
+|------|---------|
+| `.env.mobile` | Endpoints baked into the **mobile** bundle (`build:mobile`) |
+| `.env.production` | Web prod deploys (`build` / `build:prod`) |
+| `.env.beta` | Web beta deploys |
+
+Default `.env.mobile` matches production (`chatbackend.aimloperations.com`). Point it at beta to flip the shell without touching web deploys. Optional gitignored override: `.env.mobile.local`.
+
+## Versioning
+
+In `android/app/build.gradle`:
+
+- **versionName** — user-visible string; keep aligned with `package.json` `version` (currently `0.1.0`)
+- **versionCode** — integer; **must increase** for every Play Store upload
+
+Bump both before each store release.
+
+## Icons / splash
+
+Source art lives in `llm-fe/assets/` (`icon.png`, `splash.png`, `splash-dark.png`). Regenerate Android densities:
+
+```bash
+npm run assets:generate
+```
+
+## Signing (upload keystore)
+
+**Never commit keystores.** Store outside the repo (e.g. host secrets / password manager).
+
+```bash
+keytool -genkey -v -keystore ~/Documents/secrets/aiml-chat-upload.jks \
+  -keyalg RSA -keysize 2048 -validity 10000 \
+  -alias aiml-chat-upload
+```
+
+Create `llm-fe/android/keystore.properties` (gitignored):
+
+```properties
+storeFile=/absolute/path/to/aiml-chat-upload.jks
+storePassword=...
+keyAlias=aiml-chat-upload
+keyPassword=...
+```
+
+Release App Bundle:
+
+```bash
+cd llm-fe/android
+./gradlew bundleRelease
+# → app/build/outputs/bundle/release/app-release.aab
+```
+
+Debug APK (no signing props needed):
+
+```bash
+./gradlew assembleDebug
+```
+
+## Manual QA checklist
+
+On emulator **and** physical device:
+
+- [ ] Login / logout / password reset flows
+- [ ] Chat streaming + markdown / code blocks
+- [ ] Charts (`recharts`)
+- [ ] Dark / light theme
+- [ ] Hardware back: navigates history, exits at root
+- [ ] Keyboard does not cover compose input; notch/safe-area OK
+- [ ] Background → resume keeps or reconnects WebSocket
+- [ ] Airplane mode → restore reconnects
+
+## Play Store (internal testing first)
+
+Out of band ops (not automated here):
+
+1. Google Play developer account
+2. Privacy policy URL (product site / legal)
+3. Data safety form (JWT auth, chat content, analytics if Tianji runs in WebView)
+4. Screenshots for phone (+ tablet if targeting)
+5. Upload `.aab` to **internal testing** track before production
+
+## Related issues
+
+- [#20](https://git.aimloperations.com/ai_ml_operations/chat_web_app/issues/20) — this Android wrap
+- [#21](https://git.aimloperations.com/ai_ml_operations/chat_web_app/issues/21) — iOS (reuses this scaffolding)
+- [#22](https://git.aimloperations.com/ai_ml_operations/chat_web_app/issues/22) / [#23](https://git.aimloperations.com/ai_ml_operations/chat_web_app/issues/23) / [#24](https://git.aimloperations.com/ai_ml_operations/chat_web_app/issues/24) — auth / WS / routing