feat(library): update, rescan and stop on the folder menu, queued per roll

A folder row now asks for the rest of a roll, the whole of it from the top,
or takes its request back. Requests queue behind the reading in flight and
run one at a time; a row waiting its turn draws a ring that does not turn.

docker/frontend/src/i18n/en.ts

@@ -244,9 +244,10 @@ export const en: Dict = {
   'lib.rename': 'RENAME FOLDER',
   'lib.renameAsk': 'Name shown for this folder (the folder on the disk is not renamed):',
   'lib.update': 'UPDATE...',
+  'lib.rescan': 'RESCAN FROM THE TOP',
   'lib.remove': 'REMOVE',
   'lib.reconnect': 'GRANT ACCESS AGAIN',
-  'lib.nodeHint': 'Right-click to rename, update, collapse or remove the folder.',
+  'lib.nodeHint': 'Right-click to rename, update, rescan, collapse or remove the folder.',
   'lib.collapseAll': 'COLLAPSE ALL',
   'lib.collapse': 'COLLAPSE',
   'lib.colHint': 'Right-click the empty part of this column to add a folder.',