docs(kit): pin core 1.19.0; teach the public demo's module members

The pin moves 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 §10
step 3). The chapters were read again for both versions:

- Chapter 2: a new section on a public demo site, covering demoLocks in
  module.json, ctx.demoMode and api.onDemoSeed (1.18.0). The call count
  becomes twenty.
- Chapter 5: a paragraph on an event action's demoRefuses (1.19.0), and
  a line in the action listing.

The one other core change in the window (website#221) is a wording fix
on core's Teams panel and nothing a module sees. The template declares
none of the new members, so template/module.json's coreApi becomes
^1.19.0 for the equality check only.

Checks run at the new pin:
- checkCoreApi, links, rename sites and chapter paths all pass, and so
  do the script tests (10 and 11).
- The template's imports, build, externals and swagger checks pass.
- Tests pass: server 82, client 20.
- The template was loaded as `examplegame` into a real core at this ref
  through core's own loader, with DEMO_MODE unset and with it true, and
  it registered both times.

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

template/module.json

@@ -2,7 +2,7 @@
   "id": "examplegame",
   "name": "Example Game",
   "version": "0.1.0",
-  "coreApi": "^1.17.0",
+  "coreApi": "^1.19.0",
   "server": "server/index.js",
   "client": { "entry": "client/dist/entry.js" },
   "schema": "server/db/schema.sql",