Fix bash script errors: shebangs, duplicate function, missing error messages

[Copilot]

Several bash scripts had syntax and structural issues that would cause runtime problems.

Fixes

• Invalid shebangs in scripts/download_utils.sh and scripts/props.sh — double # prefix (##!/usr/bin/env bash → #!/usr/bin/env bash)
• Duplicate SILENT() function in scripts/logs.sh — removed redundant definition
• Missing ERROR_EXIT arguments in scripts/useful_utils.sh — GET_FEAT_STATUS() called ERROR_EXIT without messages

# Before
ERROR_EXIT

# After  
ERROR_EXIT "Variable '$var_name' is not defined"

All scripts now pass bash -n syntax validation.

Original prompt

Analiza los scripts y corrije erroees

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