[ENG-27] Don't silently fail the examples download when unzip is missing

[zanjonke]

Closes ENG-27.

Problem

On an image without unzip (e.g. python:3.12-slim), examples.sh printed Extracting to ... and then died with exit 127 and no message: unzip's stderr went to /dev/null, and set -euo pipefail exited before the if [ $? -eq 0 ] check could run. Because install.sh runs the script as a plain command, the whole installer went down with it, skipping the final verification and summary.

The same unreachable cmd 2>/dev/null; if [ $? ... ] pattern was used for mkdir and curl.

Changes

• Check for unzip (Expand-Archive on PowerShell) before anything is downloaded, and explain how to install it plus where else to get the examples.
• Every failure path now requires an acknowledgement (Continue? Press [Enter] to acknowledge:) so the message isn't cleared away by the installer's next step. The "failed to create directory" case previously had no prompt at all.
• Real if ! cmd checks instead of the $? patterns; a failed extraction shows the extractor's own error (capped at 3 lines) instead of discarding it.
• A download that isn't a zip (server error page) is reported as such rather than handed to the extractor.
• The optional examples step can no longer abort the installer — || echo ... in bash, try/catch in install.ps1, where & $scriptPath propagates terminating errors into the parent under $ErrorActionPreference = 'Stop' (verified).
• Prompts fall back to stdin when there is no controlling terminal, and clear can't abort the script.

Testing

Manually, in Docker with a pty, both with and without the extractor:

• bash / unzip present → examples extracted, all 8 example .sh scripts still executable
• bash / unzip absent → guidance + acknowledgement, installer runs to You're all set!, exit 0
• PowerShell 7.6 / Expand-Archive present → examples extracted
• PowerShell 7.6 / module removed → guidance + acknowledgement, exit 0

Also checked the failed-download and non-zip-download paths, and full install.sh runs end to end. Note the PowerShell runs were pwsh-on-Linux, so Windows-specific path/permission behaviour is untested.

[NejcS]

Looks good