feat: prisma schema, groups API, deploy workflow

app/server/api/groups/[id]/join.post.ts

@@ -0,0 +1,17 @@
+import { requireAuth } from '~/server/utils/auth'
+import { groups, userGroups } from '~/server/utils/db'
+
+export default defineEventHandler(async (event) => {
+  const user = requireAuth(event)
+  const groupId = getRouterParam(event, 'id')!
+
+  const group = groups.get(groupId)
+  if (!group) throw createError({ statusCode: 404, message: 'Group not found' })
+  if (!group.isPublic) throw createError({ statusCode: 403, message: 'Group is private' })
+
+  const key = `${user.id}-${groupId}`
+  if (userGroups.has(key)) return { message: 'Already a member' }
+
+  userGroups.set(key, { userId: user.id, groupId, role: 'member', joinedAt: new Date().toISOString() })
+  return { success: true, message: `Joined group "${group.name}"` }
+})