feat(files): API tokens in Settings, the Hub folder in Files, a notice before a token runs out

Settings gains an API tokens tab: a row per token (name and prefix; each
folder with its rights; last use and expiry, "expires soon" marked),
revoked from its menu behind a confirm. A new token is the Hub exchange in
one click, or folders and rights picked per folder (no Write where an
upload cannot land); expiry 30/90 days, 1 year or never (warned). The
token shows once in the same dialog, with Copy and a ready curl line.

The Hub folder closes the Sources in the Files rail, takes uploads and
moved-in files. A token about to run out warns its user once, a week
before (the Files GC's sixth pass); the notice opens the tokens tab.

frontend/src/lib/queryKeys.ts

@@ -70,6 +70,7 @@ export const qk = {
   fileFolders: () => ["file-folders"] as const,
   filePreview: (id: number) => ["file-preview", id] as const,
   storageUsage: () => ["storage-usage"] as const,
+  apiTokens: () => ["api-tokens"] as const,
   // --- downloads ---
   downloads: () => ["downloads"] as const,
   downloadIndex: () => ["download-index"] as const,