feat: add media folder management from WebUI

- Add media_folders_management config flag (enabled by default)
- Guard folder CRUD endpoints with 403 when management disabled
- Wire up frontend folder add/edit/delete in Settings tab
- Add per-folder availability check (for network shares)
- Show unavailable badge on offline folders in browser view
- Expose management flag via /api/health endpoint
- Add EN/RU locale keys for folder management UI

media_server/static/js/app.js

@@ -57,6 +57,7 @@ import {
     onBrowserSearch, clearBrowserSearch, onItemsPerPageChanged,
     downloadFile, closeFolderDialog, saveFolder,
     showManageFoldersDialog,
+    showAddFolderDialog, showEditFolderDialog, deleteFolderConfirm,
 } from './browser.js';
 
 import {
@@ -117,6 +118,7 @@ Object.assign(window, {
     onBrowserSearch, clearBrowserSearch, onItemsPerPageChanged,
     downloadFile, closeFolderDialog, saveFolder,
     showManageFoldersDialog,
+    showAddFolderDialog, showEditFolderDialog, deleteFolderConfirm,
     // Links
     showAddLinkDialog, showEditLinkDialog, closeLinkDialog,
     saveLink, deleteLinkConfirm,
@@ -323,6 +325,24 @@ window.addEventListener('DOMContentLoaded', async () => {
         else if (action === 'delete') deleteCallbackConfirm(name);
     });
 
+    // Folder dialog backdrop click to close
+    const folderDialog = document.getElementById('folderDialog');
+    folderDialog.addEventListener('click', (e) => {
+        if (e.target === folderDialog) {
+            closeFolderDialog();
+        }
+    });
+
+    // Delegated click handlers for folder table actions
+    document.getElementById('foldersTableBody').addEventListener('click', (e) => {
+        const btn = e.target.closest('[data-action]');
+        if (!btn) return;
+        const action = btn.dataset.action;
+        const folderId = btn.dataset.folderId;
+        if (action === 'edit') showEditFolderDialog(folderId);
+        else if (action === 'delete') deleteFolderConfirm(folderId);
+    });
+
     // Link dialog backdrop click to close
     const linkDialog = document.getElementById('linkDialog');
     linkDialog.addEventListener('click', (e) => {
@@ -352,7 +372,7 @@ window.addEventListener('DOMContentLoaded', async () => {
 
     // Initialize browser toolbar and load folders
     initBrowserToolbar();
-    if (token) {
+    if (!authReq || token) {
         loadMediaFolders();
     }