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.

UPGRADE.md

@@ -241,6 +241,16 @@ MONGO_CONTAINER=tcef-mongo7 MONGO_SHELL=mongosh MONGO_PORT=27019 ./smoke/smoke.s
   async, `users.findOneAsync` for the username. `onCommentAdd` mail fan-out:
   `users.find().forEach` → `forEachAsync`. Still fire-and-forget from the
   insert. Comments UI staging verification pending (pre-existing note below).
+- ✅ **fixtures.js re-enabled** — `@cleverbeagle/seeder` (sync Mongo, no Meteor
+  3 support) **removed from package.json** and replaced with a small in-repo
+  async seeder: idempotent, dev-only (staging opts in with `TCEF_SEED=1`);
+  same accounts as before (`admin@admin.com` / 5 test users / 5 Documents
+  each). Verified: `fixtures: 6 dev users ensured` on boot.
+- ✅ **sitemaps.js re-enabled** — `gadicohen:sitemaps` (pre-0.9 API, dead on
+  Meteor 3) **removed from .meteor/packages**; `/sitemap.xml` is now a small
+  `WebApp.connectHandlers` handler serving the same static page list (the
+  per-fire section of the old handler was behind `firesMapEnabled = false`,
+  i.e. dead code, and was dropped). Verified serving on dev.
 
 ### Still TODO before the web (not just REST) is fully deployable on 3.x
 - **React 16 → 18** render root + verify ancient react-* libs.