Debian packaging: strip CRLF in maintainer scripts and relax libsagui dependency

[Al-Muhandis]

Motivation

• Prevent maintainer scripts from failing due to Windows CRLF line endings when copied into the Debian staging tree.
• Make libsagui an optional recommended package instead of a hard dependency while still ensuring it is present at post-install configuration time.
• Add package metadata Origin to the control file.

Description

• Added normalize_maintainer_scripts() to build-deb.sh to strip \r line endings from DEBIAN/postinst and DEBIAN/postrm and call it after copying the debian directory into the staging tree.
• Updated debian/DEBIAN/control to remove libsagui from Depends, add it under Recommends as libsagui2 | libsagui, and include an Origin field.
• Enhanced debian/DEBIAN/postinst with a libsagui_available() check that uses ldconfig -p and added a pre-configuration validation that exits with an instructive error if the shared library is not found.

Testing

• Ran the packaging script ./build-deb.sh to recreate the staging tree and confirm the maintainer scripts were normalized and staged files were created (succeeded).
• Performed a shell syntax check with bash -n on the modified build-deb.sh and debian/DEBIAN/postinst scripts (succeeded).

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Codex Task