docs: correct the sizes the 4 KiB rebuild produced

The databases came out of the first 4 KiB build at 288.6 MB and 237.7
MB, against the 302 and 247 the registry carried. That figure is a build
guard and is also shown to the user before the SQL tab opens, so both
uses were wrong by the same 5%.

The gzip variant the host builds for the HEAD request is now 64 MB, and
the published size claims in the deployment and architecture notes
follow the same rebuild.

web/src/lib/db-probe.js

@@ -3,8 +3,8 @@
  *
  * `sql.js-httpvfs` sizes a file with a HEAD request. That request carries no
  * Range header, so the browser advertises gzip, and GitHub Pages answers with
- * `Content-Encoding: gzip` and the length of the *compressed* body — 66 MB for
- * a 302 MB database. The library rightly refuses to believe it and gives up
+ * `Content-Encoding: gzip` and the length of the *compressed* body — 64 MB for
+ * a 288 MB database. The library rightly refuses to believe it and gives up
  * with "Length of the file not known. It must either be supplied in the config
  * or given by the HTTP server."
  *