feat(settings): upload a Google Takeout export in Settings › Account

A "YouTube history" section under YouTube access: the watch history and
the Watch later csv are dropped or picked (one request each, each file's
outcome said on its own), and the section then says what the import did
- only the counts it produced - or that it is running, failed or was cut
off by a restart. While it runs it asks again until it ends; a failed
re-read shows the failure, not the previous answer.

The drop zone the Files upload had inline is now ui/DropZone, used by
both. The e2e seed clears the account's kept Takeout videos.

frontend/src/lib/queryKeys.ts

@@ -129,6 +129,7 @@ export const qk = {
   comfortPins: (lang?: string) => ["comfort-pins", ...(lang ? [lang] : [])] as const,
   plex: () => ["plex"] as const,
   plexWatchLink: () => ["plex-watch-link"] as const,
+  takeout: () => ["takeout"] as const,
   plexLibrary: (...rest: unknown[]) => ["plex-library", ...rest],
   // Discover surface: the rail payload keyed by scope+lang; `plexDiscover()` (no args) matches it and
   // the Surprise draw below for a prefix invalidation after a watched-toggle.