feat: pre-registrant management and invitation system

Admin interface to review, filter, and batch-invite the 95 pre-registrants
from Baby Ghosts. Accept-invitation page pre-fills their data and collects
circle, pronouns, motivation, contribution tier, and agreement before
creating their member record.

server/models/preRegistration.js

@@ -0,0 +1,32 @@
+import mongoose from "mongoose";
+
+const preRegistrationSchema = new mongoose.Schema(
+  {
+    email: {
+      type: String,
+      required: true,
+      unique: true,
+      lowercase: true,
+      trim: true,
+    },
+    name: String,
+    city: String,
+    role: String, // professional role (e.g. "3D artist") — admin-only reference
+    newsletterOptIn: Boolean,
+    status: {
+      type: String,
+      enum: ["pending", "selected", "invited", "accepted", "expired"],
+      default: "pending",
+    },
+    inviteEmailSentAt: Date,
+    acceptedAt: Date,
+    memberId: { type: mongoose.Schema.Types.ObjectId, ref: "Member" },
+    magicLinkJti: String,
+    magicLinkJtiUsed: { type: Boolean, default: false },
+    adminNotes: String,
+  },
+  { timestamps: true }
+);
+
+export default mongoose.models.PreRegistration ||
+  mongoose.model("PreRegistration", preRegistrationSchema);