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/api/facade.test.ts

@@ -33,6 +33,7 @@ const SLICE_MODULES = [
   ["plexApi", () => import("./plex")],
   ["downloadsApi", () => import("./downloads")],
   ["filesApi", () => import("./files")],
+  ["tokensApi", () => import("./tokens")],
   ["diagnosticsApi", () => import("./diagnostics")],
   ["debugSessionsApi", () => import("./diagnostics")],
 ] as const;