Deploy chat_web_app via server-infra (node-static) (#15)

## Summary

Implements [chat_web_app#13](#13) Part A: wire the CRA frontend into the same **node-static** deploy path as `dta_webapp` (no Docker for serving).

- `build:prod` / `build:beta` write into `/var/www/{env}.chat.aimloperations/html`
- API/WS URLs come from `REACT_APP_*` (`.env.production` / `.env.beta`) instead of hardcoded localhost
- Gitea unit tests + auto deploy-prod on `master`; deploy-beta via `workflow_dispatch`
- README documents local dev, env files, and webroot layout

Branch includes the #11 unit-test commit (`test:ci`) so CI has a green suite.

Companion server-infra branch (Part B): `issue-13-register-chat-web-app` on `ai_ml_operations/server-infra`.

## Test plan

- [ ] `cd llm-fe && npm run test:ci`
- [ ] Merge + ensure Unit Tests workflow passes on PR
- [ ] Merge server-infra `issue-13-register-chat-web-app`, then sync/pull on runner
- [ ] Redeploy web-static (or full host provision) so nginx listens on **8082**
- [ ] Manual: `server-infra/scripts/deploy.sh --app chat_web_app --env prod --ref <sha>`
- [ ] NPM: point `chat.aimloperations.com` at `adama:8082` + `roslin:8082` + `ai-server-4080:8082`
- [ ] Confirm built assets hit `https://chatbackend.aimloperations.com`Reviewed-on: #15

llm-fe/package.json

@@ -40,6 +40,8 @@
   "scripts": {
     "start": "NODE_ENV=development react-scripts start",
     "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/",
     "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"