Fix checkforupdates.sh: remove set -e and invalid snap refresh flag

[Copilot]

set -e combined with an invalid snap refresh --stable flag caused the script to abort before running Flatpak updates or printing the completion message.

Changes

checkforupdates.sh

• Removed set -e
• Fixed snap refresh --stable → snap refresh (--stable is not a valid flag)
• Wrapped Snap and Flatpak refresh in explicit error checks — failures emit a warning and execution continues

if ! snap refresh; then
    echo "Warning: Snap refresh encountered errors, continuing..."
fi

README.md

• Updated checkforupdates feature description and troubleshooting section to reflect that Snap/Flatpak failures are non-fatal

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