Vendor Chatwoot Vue 3 frontend into frontend/

Copy the Chatwoot (v4.14.0) frontend runnable subset into frontend/ for
customization:
- app/javascript/ (Vue SPA: dashboard, widget, sdk, portal, superadmin)
- app/views/ (ERB templates for vite-plugin-ruby entrypoint resolution)
- app/helpers/, app/assets/ (Rails view helpers, static assets)
- enterprise/ (Enterprise edition frontend overlay)
- config/vite.json, vite.config.ts, bin/vite (Vite-Rails toolchain)
- package.json, pnpm-lock.yaml, tailwind/postcss/eslint configs
- Gemfile, Gemfile.lock (vite_rails gem for bin/vite binstub)

Excluded Rails backend: controllers, models, services, jobs, mailers,
policies, db, lib, spec, public, node_modules.

Update references to the new frontend location:
- .gitignore: exclude frontend build artifacts (node_modules, tmp, packs),
  keep frontend/bin/ and frontend/vendor/ via negation
- backend/scripts/parity_frontend_smoke.sh: CHATWOOT_DIR default
  reference/chatwoot -> ../frontend
- backend/scripts/parity_frontend_browser_smoke.mjs: same default update
- AGENTS.md: add frontend section with Rails/Vite coupling notes
- README: architecture tree includes frontend/

frontend/app/javascript/dashboard/components/widgets/conversation/helpers/specs/emailHeadHelper.spec.js

@@ -0,0 +1,16 @@
+import { validEmailsByComma } from '../emailHeadHelper';
+
+describe('#validEmailsByComma', () => {
+  it('returns true when empty string is passed', () => {
+    expect(validEmailsByComma('')).toEqual(true);
+  });
+  it('returns true when valid emails separated by comma is passed', () => {
+    expect(validEmailsByComma('ni@njan.com,po@va.da')).toEqual(true);
+  });
+  it('returns false when one of the email passed is invalid', () => {
+    expect(validEmailsByComma('ni@njan.com,pova.da')).toEqual(false);
+  });
+  it('strips spaces between emails before validating', () => {
+    expect(validEmailsByComma('1@test.com  , 2@test.com')).toEqual(true);
+  });
+});

frontend/app/javascript/dashboard/components/widgets/conversation/helpers/specs/scrollTopCalculationHelper.spec.js

@@ -0,0 +1,18 @@
+import { calculateScrollTop } from '../scrollTopCalculationHelper';
+
+describe('#calculateScrollTop', () => {
+  it('returns calculated value of the scrollTop property', () => {
+    class DOMElement {
+      constructor(scrollHeight) {
+        this.scrollHeight = scrollHeight;
+      }
+    }
+    let count = 3;
+    let relevantMessages = [];
+    while (count > 0) {
+      relevantMessages.push(new DOMElement(100));
+      count -= 1;
+    }
+    expect(calculateScrollTop(1000, 300, relevantMessages)).toEqual(550);
+  });
+});