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/api/admin/members/[id]/role.patch.js

@@ -0,0 +1,35 @@
+import Member from '../../../../models/member.js'
+import { connectDB } from '../../../../utils/mongoose.js'
+import { validateBody } from '../../../../utils/validateBody.js'
+import { adminRoleUpdateSchema } from '../../../../utils/schemas.js'
+
+export default defineEventHandler(async (event) => {
+  const admin = await requireAdmin(event)
+  await connectDB()
+
+  const { role } = await validateBody(event, adminRoleUpdateSchema)
+  const memberId = getRouterParam(event, 'id')
+
+  // Prevent self-demotion
+  if (admin._id.toString() === memberId && role !== 'admin') {
+    throw createError({
+      statusCode: 400,
+      statusMessage: 'You cannot remove your own admin role.'
+    })
+  }
+
+  const member = await Member.findByIdAndUpdate(
+    memberId,
+    { role },
+    { new: true }
+  )
+
+  if (!member) {
+    throw createError({
+      statusCode: 404,
+      statusMessage: 'Member not found.'
+    })
+  }
+
+  return { success: true, member }
+})