Ship Android app by wrapping the web build with Capacitor (#20) (#28)

## Summary
- Closes #20
- Add Capacitor 7 to `llm-fe/` (`capacitor.config.ts`, appId `com.aimloperations.chat`, `webDir: build`) and commit the generated `android/` project
- npm scripts: `build:mobile` (`.env.mobile` + CRA build + `cap sync`), `android:open`, `android:sync`, `assets:generate`
- `.env.mobile` defaults to prod backend; override independently of web deploys
- Native chrome: Android back button (history / exit at root), status bar + keyboard resize, safe-area CSS; Preferences registered for JWT mirror (#22)
- Icons/splash via `@capacitor/assets`; signing via optional `keystore.properties`; docs in `llm-fe/ANDROID.md` + root README

Blockers #22 / #23 / #24 already on master.

## Test plan
- [x] `npm run test:ci` (79 tests)
- [x] `npm run build` + `npx cap add android` / `cap sync`
- [ ] `npm run build:mobile` + open in Android Studio on a machine with SDK
- [ ] Emulator/device QA: login, chat stream, theme, back button, keyboard/safe-area, WS resume
- [ ] Generate upload keystore outside repo; `./gradlew bundleRelease` for internal testing trackReviewed-on: #28

llm-fe/public/index.html

@@ -6,7 +6,7 @@
   <link rel="icon" href="%PUBLIC_URL%/favicon.ico" sizes="any" />
   <link rel="icon" type="image/png" sizes="32x32" href="%PUBLIC_URL%/favicon-32x32.png" />
   <link rel="icon" type="image/png" sizes="16x16" href="%PUBLIC_URL%/favicon-16x16.png" />
-  <meta name="viewport" content="width=device-width, initial-scale=1" />
+  <meta name="viewport" content="width=device-width, initial-scale=1, viewport-fit=cover" />
   <meta name="theme-color" content="#000000" />
   <meta name="description" content="Hesychia — a calm AI assistant by AI ML Operations, LLC" />
   <meta name="application-name" content="Hesychia" />