meteor3: re-enable fixtures and sitemaps with async/Meteor-3 implementations

fixtures: drop @cleverbeagle/seeder (sync Mongo, unmaintained) for a small
idempotent async seeder (same dev accounts). sitemaps: drop dead
gadicohen:sitemaps for a WebApp.connectHandlers /sitemap.xml with the same
static page list (the per-fire section was already disabled). Verified on
dev boot: 6 users ensured, sitemap serving; REST smoke byte-identical.

package.json

@@ -8,7 +8,6 @@
   "dependencies": {
     "@babel/runtime": "^7.29.7",
     "@cleverbeagle/dates": "^0.5.1",
-    "@cleverbeagle/seeder": "^1.3.1",
     "@turf/buffer": "^5.1.5",
     "babel-runtime": "^6.26.0",
     "bcrypt": "^1.0.3",