feat: onboarding optimization, invite links, admin roles, and event board

- Home: hide duplicate create/join buttons when user has no groups
- Invite links: /join/group/:id and /join/team/:id pages for one-click joining
- Admin: group admins field, ownership transfer, member management toggle
- Events: new events collection with RSVP (going/interested/maybe) and comments

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/pb_migrations/1776760462_updated_groups.js

@@ -0,0 +1,45 @@
+/// <reference path="../pb_data/types.d.ts" />
+migrate((db) => {
+  const dao = new Dao(db)
+  const collection = dao.findCollectionByNameOrId("es63bkyiblpnxdf")
+
+  // add admins field
+  collection.schema.addField(new SchemaField({
+    "system": false,
+    "id": "sf_admins",
+    "name": "admins",
+    "type": "relation",
+    "required": false,
+    "presentable": false,
+    "unique": false,
+    "options": {
+      "collectionId": "_pb_users_auth_",
+      "cascadeDelete": false,
+      "minSelect": null,
+      "maxSelect": null,
+      "displayFields": null
+    }
+  }))
+
+  // add allowMemberManage field
+  collection.schema.addField(new SchemaField({
+    "system": false,
+    "id": "sf_allowmm",
+    "name": "allowMemberManage",
+    "type": "bool",
+    "required": false,
+    "presentable": false,
+    "unique": false,
+    "options": {}
+  }))
+
+  return dao.saveCollection(collection)
+}, (db) => {
+  const dao = new Dao(db)
+  const collection = dao.findCollectionByNameOrId("es63bkyiblpnxdf")
+
+  collection.schema.removeField("sf_admins")
+  collection.schema.removeField("sf_allowmm")
+
+  return dao.saveCollection(collection)
+})