refactor(frontend): migrate off deprecated Ant Design 6 props

The repo's type-aware deprecation sweep (eslint.deprecated.config.js) reported fourteen findings; it now reports zero. Alert message becomes title and closable+onClose becomes closable.onClose; Select optionFilterProp moves into showSearch.optionFilterProp and suffixIcon becomes suffix; Drawer width becomes size; Progress trailColor becomes railColor. Behavior is unchanged apart from a few single-mode selects gaining type-to-filter, which the old prop already implied.

frontend/src/pages/sub/SubPage.tsx

@@ -286,7 +286,7 @@ export default function SubPage() {
             <Col xs={24} sm={22} md={18} lg={14} xl={12}>
               <Card hoverable className="subscription-card" title={cardTitle} extra={cardExtra}>
                 {announce && (
-                  <Alert type="info" showIcon message={announce} style={{ marginBottom: 16 }} />
+                  <Alert type="info" showIcon title={announce} style={{ marginBottom: 16 }} />
                 )}
                 <Descriptions
                   bordered