Refactor email templates to use plain text format and update sender addresses

- Simplified the magic link email format to plain text for better compatibility.
- Updated the welcome email to use plain text and changed the sender address to match the domain.
- Enhanced event registration email format to plain text, removing HTML styling for a cleaner approach.

server/utils/schemas.js

@@ -326,3 +326,7 @@ export const adminMemberCreateSchema = z.object({
   circle: z.enum(['community', 'founder', 'practitioner']),
   contributionTier: z.enum(['0', '5', '15', '30', '50'])
 })
+
+export const adminRoleUpdateSchema = z.object({
+  role: z.enum(['admin', 'member'])
+})