perf(wallets): walk added wallet folders off the UI thread

Every open of the Wallets dialog, Refresh, folder add or remove, and Open
on a stale row walked each user-added folder recursively on the UI thread
before the dialog drew: up to 40,000 entries per folder, roughly
50-150 ms warm on Linux and seconds on a cold disk, a network share or
Windows.

The datadir listing (a few top-level files) stays synchronous, so a
wallet just created shows at once. The recursive walk runs on a detached
worker with the same depth, hit and entry limits; its rows are merged at
the start of a later frame and only the new rows are probed.

- The dialog opens at once with the datadir rows. The external rows
  arrive when the walk ends, with "Scanning folders..." beside the
  scanned-folders caption, and the card grows once.
- Reopening within 60 s with the same folders reuses the last walk
  without touching the disk, so its rows and sizes can be up to a minute
  stale: a wallet copied into a folder in that minute needs Refresh.
  Refresh and Open on a stale row always walk again.
- While a walk or a wallet probe runs (up to 30 s) the dialog keeps
  frames coming, so rows and badges appear without moving the mouse.
- The 200-row cap now holds across all folders; each extra folder could
  add one row past it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

res/lang/de.json

@@ -2304,6 +2304,7 @@
     "wallets_reveal": "Ordner anzeigen",
     "wallets_scan_folder": "Einen weiteren Ordner nach Wallets durchsuchen…",
     "wallets_scanned_folders": "Durchsuchte Ordner:",
+    "wallets_scanning": "Ordner werden durchsucht…",
     "wallets_sort_addresses": "Adressen",
     "wallets_sort_asc": "Aufsteigend (ältestes / wenigste / kleinstes zuerst)",
     "wallets_sort_by": "Sortieren:",

res/lang/es.json

@@ -2304,6 +2304,7 @@
     "wallets_reveal": "Mostrar carpeta",
     "wallets_scan_folder": "Escanear otra carpeta en busca de carteras…",
     "wallets_scanned_folders": "Carpetas escaneadas:",
+    "wallets_scanning": "Buscando en las carpetas…",
     "wallets_sort_addresses": "Direcciones",
     "wallets_sort_asc": "Ascendente (más antiguo / menos / más pequeño primero)",
     "wallets_sort_by": "Ordenar:",

res/lang/fr.json

@@ -2304,6 +2304,7 @@
     "wallets_reveal": "Afficher le dossier",
     "wallets_scan_folder": "Analyser un autre dossier pour des portefeuilles…",
     "wallets_scanned_folders": "Dossiers analysés :",
+    "wallets_scanning": "Analyse des dossiers…",
     "wallets_sort_addresses": "Adresses",
     "wallets_sort_asc": "Croissant (plus ancien / moins / plus petit d'abord)",
     "wallets_sort_by": "Trier :",

res/lang/ja.json

@@ -2304,6 +2304,7 @@
     "wallets_reveal": "フォルダを開く",
     "wallets_scan_folder": "別のフォルダをスキャンしてウォレットを検索…",
     "wallets_scanned_folders": "スキャン対象フォルダー：",
+    "wallets_scanning": "フォルダをスキャンしています…",
     "wallets_sort_addresses": "アドレス",
     "wallets_sort_asc": "昇順（古い/少ない/小さい順）",
     "wallets_sort_by": "並べ替え：",

res/lang/ko.json

@@ -2304,6 +2304,7 @@
     "wallets_reveal": "폴더 열기",
     "wallets_scan_folder": "다른 폴더에서 지갑 검색…",
     "wallets_scanned_folders": "스캔한 폴더:",
+    "wallets_scanning": "폴더 검색 중…",
     "wallets_sort_addresses": "주소",
     "wallets_sort_asc": "오름차순 (오래된/적은/작은 순)",
     "wallets_sort_by": "정렬:",

res/lang/pt.json

@@ -2304,6 +2304,7 @@
     "wallets_reveal": "Mostrar pasta",
     "wallets_scan_folder": "Escanear outra pasta em busca de carteiras…",
     "wallets_scanned_folders": "Pastas verificadas:",
+    "wallets_scanning": "Procurando nas pastas…",
     "wallets_sort_addresses": "Endereços",
     "wallets_sort_asc": "Crescente (mais antigo / menos / menor primeiro)",
     "wallets_sort_by": "Ordenar:",

res/lang/ru.json

@@ -2304,6 +2304,7 @@
     "wallets_reveal": "Открыть папку",
     "wallets_scan_folder": "Сканировать другую папку на наличие кошельков…",
     "wallets_scanned_folders": "Просканированные папки:",
+    "wallets_scanning": "Поиск в папках…",
     "wallets_sort_addresses": "Адреса",
     "wallets_sort_asc": "По возрастанию (сначала старые / меньше / меньший)",
     "wallets_sort_by": "Сортировка:",

res/lang/zh.json

@@ -2304,6 +2304,7 @@
     "wallets_reveal": "打开文件夹",
     "wallets_scan_folder": "扫描其他文件夹以查找钱包…",
     "wallets_scanned_folders": "已扫描的文件夹：",
+    "wallets_scanning": "正在扫描文件夹…",
     "wallets_sort_addresses": "地址",
     "wallets_sort_asc": "升序（最早/最少/最小优先）",
     "wallets_sort_by": "排序：",