fix(ci): restore the missing comma in core-ref.json

The template job's "Clone core at the pinned ref" step reads the pin with
require('./ci/core-ref.json'), and the file has not parsed since
0678047 (2026-10-06): the "why" array lost the comma after "Before that
move:". So the job has failed on every PR since, run 15 and run 16 (#15)
included, before it reached a single check.

The local runs missed it because checkCoreApi takes the core as
`--core .core` and never reads this file. Only the CI clone step reads
it. The file now parses, and `ref` is 6890a74 as #15 set it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E14m6SuuY6i1vASFeGDBeY

ci/core-ref.json

@@ -34,7 +34,7 @@
     "The template declares neither, and nothing it does changed meaning. The real",
     "core run below was repeated at this ref.",
     "",
-    "Before that move:"
+    "Before that move:",
     "This one is the EVENT SYSTEM cutover, the commit MODULE_API_VERSION 1.10.0",
     "reached `main` on (website#199), and 1.10.0 is what template/module.json",
     "declares. It moved here from 66bb3b9a (1.9.0, the engagement cutover) because",