refactor: extract shared utilities and standardize page patterns

- Add fmtBytes() and csvToArr() helpers to hoover/helpers.js
- Replace inline async patterns with ActionButton/ConfirmDelete in wireguard.js
- Convert addDomain/editDomain to QuickModal + apiSubmit in proxy.js
- Convert settingsModal handlers to formAction in certs.js
- Remove redundant synced handling from dhcp.js apply button
- Add onComplete callback to ConfirmDelete (fixes users.js onRefresh bug)
- Fix passkeys.js ActionCell/Table usage (invalid component API)
- Remove duplicate fmtBytes from dashboard.js

webui/static/hoover/helpers.js

@@ -56,6 +56,28 @@ export function parseZones(data) {
  * @param {Blob} blob
  * @param {string} filename
  */
+/**
+ * Format bytes to human-readable string.
+ * @param {number} bytes
+ */
+export function fmtBytes(bytes) {
+    if (bytes === 0) return '0 B';
+    const k = 1024;
+    const sizes = ['B', 'KB', 'MB', 'GB', 'TB'];
+    const i = Math.floor(Math.log(bytes) / Math.log(k));
+    return (bytes / Math.pow(k, i)).toFixed(i > 0 ? 1 : 0) + ' ' + sizes[i];
+}
+
+/**
+ * Split a comma-separated string into trimmed, non-empty values.
+ * @param {string} [value]
+ * @returns {string[]}
+ */
+export function csvToArr(value) {
+    if (!value || !value.trim()) return [];
+    return value.split(',').map(s => s.trim()).filter(Boolean);
+}
+
 export function downloadBlob(blob, filename) {
     const url = URL.createObjectURL(blob);
     const a = document.createElement('a');