quality: web debt batch (tests runner, FireContainer, rate-limit, maps, i18n)

Independent-of-prod quality debt from PENDIENTE.md §2:

- test: migrate broken Jest -> meteortesting:mocha. Tests rewritten to chai +
  Meteor 3 async APIs, moved to test/server/ (server-only). test/server/
  00-setup.test.js re-runs the collection2/accounts init that `meteor test`
  skips (no server/main.js). New comments method + mediaAnalyzers coverage.
  Dropped rest.test.js (removed meteor/http; covered by smoke/). 36 passing.
- fix: scope FireContainer read by the URL _id on the archive route instead of
  a selector-less FiresCollection.findOne() (imports/ui/pages/Fires/Fires.js).
- feat: rate-limit abusable publications via rateLimitSubscriptions (fireFrom*
  and comments.forReference 5/1000ms; geo subs 10/1000ms).
- perf: append loading=async to the Google Maps loader URL (Gkeys.js).
- deps: meteor-accounts-t9n 2.0 -> 2.6 (no gl build -> keep gl->es fallback,
  documented); add 3 missing gl/common.json keys (0 missing now).
- deps: drop jest/babel/enzyme, add chai.

imports/startup/client/i18n.js

@@ -51,6 +51,8 @@ if (sendMissing && Meteor.isDevelopment) {
 }
 
 function setT9(lang) {
+  // meteor-accounts-t9n has no Galician build, so use Spanish for gl account
+  // error messages (the closest shipped language). See common/i18n.js.
   if (lang === 'gl') {
     T9n.setLanguage('es');
   } else {