fix: system-hub API using baseclass.extend() for proper LuCI compatibility

Fixed TypeError: "factory yields invalid constructor" by:
- Adding 'require baseclass' directive
- Using baseclass.extend() to return proper constructor
- Added formatUptime() helper function
- Added formatBytes() helper function

This matches the pattern used in luci-app-secubox and other LuCI modules.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

luci-app-system-hub/htdocs/luci-static/resources/system-hub/api.js

@@ -1,6 +1,13 @@
 'use strict';
+'require baseclass';
 'require rpc';
 
+/**
+ * System Hub API
+ * Package: luci-app-system-hub
+ * RPCD object: luci.system-hub
+ */
+
 var callStatus = rpc.declare({
 	object: 'luci.system-hub',
 	method: 'status',
@@ -64,7 +71,25 @@ var callGetStorage = rpc.declare({
 	expect: { storage: [] }
 });
 
-return {
+function formatUptime(seconds) {
+	if (!seconds) return '0s';
+	var d = Math.floor(seconds / 86400);
+	var h = Math.floor((seconds % 86400) / 3600);
+	var m = Math.floor((seconds % 3600) / 60);
+	if (d > 0) return d + 'd ' + h + 'h';
+	if (h > 0) return h + 'h ' + m + 'm';
+	return m + 'm';
+}
+
+function formatBytes(bytes) {
+	if (!bytes) return '0 B';
+	var k = 1024;
+	var sizes = ['B', 'KB', 'MB', 'GB', 'TB'];
+	var i = Math.floor(Math.log(bytes) / Math.log(k));
+	return (bytes / Math.pow(k, i)).toFixed(2) + ' ' + sizes[i];
+}
+
+return baseclass.extend({
 	getStatus: callStatus,
 	getSystemInfo: callGetSystemInfo,
 	getHealth: callGetHealth,
@@ -74,5 +99,7 @@ return {
 	backupConfig: callBackupConfig,
 	restoreConfig: callRestoreConfig,
 	reboot: callReboot,
-	getStorage: callGetStorage
+	getStorage: callGetStorage,
-};
+	formatUptime: formatUptime,
+	formatBytes: formatBytes
+});