Add warning for removeConnection invoked with no selection

[Copilot]

Addresses feedback from #398 to improve user experience when removeConnection is invoked without a connection selection.

Changes

• Added ext.outputChannel.warn() when connectionsToDelete.length === 0 to inform users instead of silently returning
• Updated localization bundle with new warning string

if (connectionsToDelete.length === 0) {
    ext.outputChannel.warn(l10n.t('No connections selected to remove.'));
    return;
}

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