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

.gitea/workflows/deploy-prod.yml

@@ -0,0 +1,22 @@
+name: Deploy Prod
+
+# Runs after Unit Tests completes on master. Direct pushes only (not PRs).
+on:
+  workflow_run:
+    workflows: [Unit Tests]
+    types: [completed]
+    branches: [master]
+
+jobs:
+  deploy:
+    if: gitea.event.workflow_run.conclusion == 'success' && gitea.event.workflow_run.event == 'push'
+    runs-on: self-hosted
+    env:
+      SERVER_INFRA_ROOT: /home/westfarn/Documents/repos/server-infra
+    steps:
+      - name: Deploy chat_web_app prod
+        run: |
+          "$SERVER_INFRA_ROOT/scripts/deploy.sh" \
+            --app chat_web_app \
+            --env prod \
+            --ref "${{ gitea.event.workflow_run.head_sha }}"