fix(build): update prebuilt CoreX artifact count 13→14 — SHA256SUMS has 14 entries after corex_gdn_chunk_recurrent.so was added

install_prebuilt_corex.sh asserted exactly 13 artifacts, but SHA256SUMS
now contains 14 (corex_gdn_chunk_recurrent.so was added in 9a52f057).
This mismatch causes Docker build to fail at:
  'expected 13 prebuilt CoreX artifacts, found 14'

qwen3_6_scripts/install_prebuilt_corex.sh

@@ -16,8 +16,8 @@ MANIFEST=${BUNDLE_DIR}/SHA256SUMS
 }
 
 mapfile -t artifacts < <(awk '{print $2}' "$MANIFEST")
-[[ "${#artifacts[@]}" -eq 13 ]] || {
-    printf 'expected 13 prebuilt CoreX artifacts, found %s\n' \
+[[ "${#artifacts[@]}" -eq 14 ]] || {
+    printf 'expected 14 prebuilt CoreX artifacts, found %s\n' \
         "${#artifacts[@]}" >&2
     exit 2
 }