Add SKU column before product title

- Added SKU column as second column after checkbox
- SKU displayed in monospace font for readability
- Slightly reduced product name truncation to fit table

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

admin/class-informatiq-sp-admin.php

@@ -620,6 +620,7 @@ class Informatiq_SP_Admin {
 						<thead>
 							<tr>
 								<th style="width: 30px;"><input type="checkbox" id="informatiq-sp-select-all-header"></th>
+								<th><?php esc_html_e( 'SKU', 'informatiq-smart-pricing' ); ?></th>
 								<th><?php esc_html_e( 'Product', 'informatiq-smart-pricing' ); ?></th>
 								<th><?php esc_html_e( 'Your Price', 'informatiq-smart-pricing' ); ?></th>
 								<th><?php esc_html_e( 'Suggested', 'informatiq-smart-pricing' ); ?></th>