feat: Add rich template preview for WhatsApp & Twilio Templates (#13206)

This PR introduces a comprehensive, display-only template preview system
for both WhatsApp and Twilio templates rendering of all supported
template types.

This lays the foundation for rich template previews across:
- Template selection modals
- Campaign creation flows
- Message composer
- Message screen.

<img width="1818" height="2058" alt="template-preview"
src="https://github.com/user-attachments/assets/9833b28c-f824-4568-8f74-6da09ac61f62"
/>

---------

Co-authored-by: Sivin Varghese <64252451+iamsivin@users.noreply.github.com>
Co-authored-by: iamsivin <iamsivin@gmail.com>
Co-authored-by: Muhsin <12408980+muhsin-k@users.noreply.github.com>

app/javascript/dashboard/components-next/template-preview/index.js

@@ -0,0 +1,6 @@
+// Main Template Preview Component
+export { default as TemplatePreview } from './TemplatePreview.vue';
+
+// Core Services
+export { TemplateTypeDetector } from 'dashboard/services/TemplateTypeDetector';
+export { TemplateNormalizer } from 'dashboard/services/TemplateNormalizer';