fix(launch-flow): send welcome email on free /accept-invite activation

Free invite acceptance previously created a Member and signed them in
without sending the welcome email — pre-registrants got nothing as the
join confirmation. Wire sendWelcomeEmail into the free branch matching
the pattern in members/create.post.js.

Paid /accept-invite activations continue to receive the welcome email
via /api/helcim/subscription on the pending_payment → active transition,
so this only changes the free path.

server/api/invite/accept.post.js

@@ -5,6 +5,7 @@ import { connectDB } from '../../utils/mongoose.js'
 import { setAuthCookie } from '../../utils/auth.js'
 import { assignMemberNumber } from '../../utils/memberNumber.js'
 import { createHelcimCustomer } from '../../utils/helcim.js'
+import { sendWelcomeEmail } from '../../utils/resend.js'
 
 export default defineEventHandler(async (event) => {
   const body = await validateBody(event, inviteAcceptSchema)
@@ -88,6 +89,15 @@ export default defineEventHandler(async (event) => {
   // For free tier, redirect to welcome
   if (body.contributionAmount === 0) {
     await autoFlagPreExistingSlackAccess(member)
+    try {
+      await sendWelcomeEmail(member)
+      logActivity(member._id, 'email_sent', {
+        emailType: 'welcome',
+        subject: 'Welcome to Ghost Guild'
+      })
+    } catch (emailError) {
+      console.error('Failed to send welcome email:', emailError)
+    }
     return {
       success: true,
       requiresPayment: false,