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/services/TemplateConstants.js

@@ -0,0 +1,58 @@
+export const PLATFORMS = {
+  WHATSAPP: 'whatsapp',
+  TWILIO: 'twilio',
+};
+
+export const WA_COMPONENT_TYPES = {
+  HEADER: 'HEADER',
+  BODY: 'BODY',
+  FOOTER: 'FOOTER',
+  BUTTONS: 'BUTTONS',
+};
+
+export const WA_HEADER_FORMATS = {
+  TEXT: 'TEXT',
+  IMAGE: 'IMAGE',
+  VIDEO: 'VIDEO',
+  DOCUMENT: 'DOCUMENT',
+};
+
+export const WA_MEDIA_FORMATS = [
+  WA_HEADER_FORMATS.IMAGE,
+  WA_HEADER_FORMATS.VIDEO,
+  WA_HEADER_FORMATS.DOCUMENT,
+];
+
+export const WA_BUTTON_TYPES = {
+  COPY_CODE: 'COPY_CODE',
+};
+
+export const WA_PARAM_FORMATS = {
+  POSITIONAL: 'POSITIONAL',
+  NAMED: 'NAMED',
+};
+
+export const TWILIO_TYPE_PREFIX = 'twilio/';
+
+export const TWILIO_TYPES = {
+  TEXT: 'text',
+  MEDIA: 'media',
+  QUICK_REPLY: 'quick_reply',
+  CALL_TO_ACTION: 'call_to_action',
+  CATALOG: 'catalog',
+};
+
+export const TEMPLATE_TYPES = {
+  WHATSAPP_TEXT: 'whatsapp-text',
+  WHATSAPP_TEXT_HEADER: 'whatsapp-text-header',
+  WHATSAPP_MEDIA_IMAGE: 'whatsapp-media-image',
+  WHATSAPP_MEDIA_VIDEO: 'whatsapp-media-video',
+  WHATSAPP_MEDIA_DOCUMENT: 'whatsapp-media-document',
+  WHATSAPP_INTERACTIVE: 'whatsapp-interactive',
+  WHATSAPP_COPY_CODE: 'whatsapp-copy-code',
+  TWILIO_TEXT: 'twilio-text',
+  TWILIO_MEDIA: 'twilio-media',
+  TWILIO_QUICK_REPLY: 'twilio-quick-reply',
+  TWILIO_CALL_TO_ACTION: 'twilio-call-to-action',
+  TWILIO_CARD: 'twilio-card',
+};