docs(kit): pin core 1.20.0; teach onUserDeleting

Moves ci/core-ref.json from 69998ec (1.19.0) to 7bd93b8 (1.20.0, website#232,
account deletion). Chapter 2 gains "When a member deletes their account": the
hook runs before the row goes, a cascade is not an unlink, it cannot stop the
deletion, so a module that talks to a game needs a record and a retry. Its call
count becomes twenty-one. The demo section now says core refuses multipart bodies
and data: URIs (website#229) on module routes without them being listed. The
template's coreApi becomes ^1.20.0 for the equality check.

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

ci/core-ref.json

@@ -1,10 +1,24 @@
 {
   "repo": "https://gitea.whitlocktech.com/RunicGateway/website.git",
   "branch": "main",
-  "ref": "69998ec54854d46681def92985a2b299ee3582a6",
+  "ref": "7bd93b8bb0da734a642587f256d10c523ca39bea",
   "why": [
     "The core this kit is written against, pinned to a commit rather than a branch.",
     "",
+    "2026-10-30: moved from 69998ec (1.19.0) to 7bd93b8 (1.20.0, website#232,",
+    "account deletion, ACCOUNT_DELETION.md). Chapter 2 was read again:",
+    "- 1.20.0: api.onUserDeleting (chapter 2 gains a section, and its call count",
+    "  becomes twenty-one).",
+    "The other core changes in the window (website#225-#231) are the public",
+    "demo's deploy, seed and locks. One reaches a module: website#229 refuses, on",
+    "a demo, any write whose JSON body carries a data: URI, beside the multipart",
+    "refusal 1.18.0 already had, and neither needs listing in demoLocks. Chapter",
+    "2's demo section now says so; it had not taught the multipart one either.",
+    "The template declares none of the new members, so nothing it does changed",
+    "meaning; module.json's coreApi becomes ^1.20.0 for the equality check. The",
+    "real core run was repeated at this ref, with the template as the only",
+    "module in the directory.",
+    "",
     "2026-10-26: moved from 6890a74 (1.17.0) to 69998ec (1.19.0, website#224),",
     "past 1.18.0 (website#223). Both are the public demo (DEMO_MODE.md), and the",
     "chapters were read again for both versions:",