Keep the type check out of npm run build so installs fit in 2 GB (issue #3181)

.github/MAINTAINERS.md

@@ -88,7 +88,7 @@ npm run lint -- --fix
 **Frontend type errors:**
 ```bash
 cd frontend
-npx tsc --noEmit
+npm run typecheck
 # Fix the errors shown
 ```
 

.github/workflows/ci.yml

@@ -276,9 +276,13 @@ jobs:
         working-directory: frontend
         run: npm ci
 
+      # `tsc -b`, not `tsc --noEmit`: the root tsconfig only holds project
+      # references, so plain `tsc` checks zero files. Kept out of `npm run
+      # build` because every installer runs that on the user's machine, and
+      # the type check alone needs ~1 GB of Node heap (#3181).
       - name: Run TypeScript check
         working-directory: frontend
-        run: npx tsc --noEmit
+        run: npm run typecheck
 
   frontend-tests:
     name: Frontend Tests