Fix checksum verification failure in install.sh (related to #642)

The .sha256 files generated during release builds contained only the hash,
but sha256sum -c expects the format "hash  filename". This caused all
install.sh updates to fail with "Checksum verification failed" even when
the checksum was correct.

Root cause: build-release.sh line 289 was using awk to extract only field 1
(the hash), discarding the filename that sha256sum -c needs.

Fix: Remove the awk filter to preserve the full sha256sum output format.

This affected the demo server update workflow and user installations.

scripts/build-release.sh

@@ -286,7 +286,7 @@ if [ ${#checksum_files[@]} -eq 0 ]; then
 else
     # Generate individual .sha256 files for each asset (required by install.sh)
     for file in "${checksum_files[@]}"; do
-        sha256sum "$file" | awk '{print $1}' > "${file}.sha256"
+        sha256sum "$file" > "${file}.sha256"
     done
 
     # Also generate combined checksums.txt for convenience