feat: restructure into XFlow monorepo with Nuxt 4, Modular Onion Monolith, Android client, and Desktop CLI

apps/web/server/api/groups/[id]/join.post.ts

@@ -0,0 +1,22 @@
+import { requireAuth } from '~/server/utils/auth'
+import { prisma } from '~/server/utils/prisma'
+
+export default defineEventHandler(async (event) => {
+  const user = requireAuth(event)
+  const groupId = getRouterParam(event, 'id')!
+
+  const group = await prisma.group.findUnique({ where: { id: groupId } })
+  if (!group) throw createError({ statusCode: 404, message: 'Group not found' })
+  if (!group.isPublic) throw createError({ statusCode: 403, message: 'Group is private' })
+
+  const existing = await prisma.groupMember.findUnique({
+    where: { userId_groupId: { userId: user.id, groupId } }
+  })
+  if (existing) return { message: 'Already a member' }
+
+  await prisma.groupMember.create({
+    data: { userId: user.id, groupId, role: 'member' }
+  })
+
+  return { success: true, message: `Joined group "${group.name}"` }
+})