[Bug]: kickstart.sh local build aborts instead of falling back to .tar.gz when .tar.zst is missing (curl exit 56 unhandled)

Bug description

On macOS, kickstart always does a local build. If zstd is installed, try_build_install first downloads netdata-v2.11.1.tar.zst. The v2.11.1 release doesn't include that file (it returns 404), although netdata-v2.11.1.tar.gz and sha256sums.txt both exist. The gzip fallback never runs. My curl reported the 404 with exit code 56 rather than 22. handle_curl_result() only treats 22/78 as HTTP errors, and every other code goes to fatal "Unknown error …", which kills the script before the .gz attempt:

curl: (56) The requested URL returned error: 404
...
 ABORTED  Unknown error when downloading https://github.com/netdata/netdata/releases/download/v2.11.1/netdata-v2.11.1.tar.zst

There is also a separate cosmetic problem. The deferred warning prints printf: '{': invalid format character. deferred_warnings() passes NETDATA_WARNINGS to printf as the format string, and the warning text contains the curl --write-out "%{http_code}" argument.

Expected behavior

When the .zst download fails, the script falls back to .tar.gz as the code intends. Separately, either .tar.zst should be published for stable releases, or the script should stop requesting it.

Steps to reproduce

1. On macOS with zstd installed (Homebrew), run: sh netdata-kickstart.sh --stable-channel --claim-token <TOKEN> --claim-rooms <ROOM>
2. The script downloads build dependencies, then requests …/v2.11.1/netdata-v2.11.1.tar.zst and gets a 404.
3. curl exits with 56, and the script aborts

curl: (56) The requested URL returned error: 404
 FAILED

XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

The following non-fatal warnings or errors were encountered:

/tmp/netdata-kickstart.sh: line 499: printf: `{': invalid format character
  - Command "sh -c "${1}" --fail -q -sSL --connect-timeout 10 --retry 3 --write-out "

XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
 A FATAL ERROR WAS ENCOUNTERED!
 \/ \/ \/ \/ \/ \/ \/ \/ \/ \/

 ABORTED  Unknown error when downloading https://github.com/netdata/netdata/releases/download/v2.11.1/netdata-v2.11.1.tar.zst

Installation method

kickstart.sh

System info

Darwin There.local 25.6.0 Darwin Kernel Version 25.6.0: Fri Jul 31 19:11:03 PDT 2026; root:xnu-12377.161.14~5/RELEASE_ARM64_T8132 arm64
ProductName:		macOS
ProductVersion:		26.6.2
BuildVersion:		25G83

Netdata build info

Not applicable

Additional info

Workaround: brew unlink zstd, run the installer, then brew link zstd