feat(files): the Files page — the library in one aligned list, its folders in a rail

Files is the one library: every done file, the ones shared with me, or one
folder's, picked in a side rail (sources, own folders, the storage meter) and
mirrored to ?folder=. One table with every kind of value in its own column;
Copy link, Share and Save in sight, every action on a right click: play,
cut, rename in the row, move to an own folder or back home, keep, details,
re-download, delete.

The Downloads page keeps only the queue until the tray replaces it. The old
/api/downloads library routes are gone: list shared, upload, the details
PATCH, delete, the file and the usage now live under /api/files, and a
listed file says which source it came from. The job's "expired" flag is gone
with the state it described.

frontend/src/lib/api.ts

@@ -60,6 +60,8 @@ export {
 } from "./api/plex";
 import { downloadsApi } from "./api/downloads";
 export type * from "./api/downloads";
+import { filesApi } from "./api/files";
+export type * from "./api/files";
 import { debugSessionsApi, diagnosticsApi } from "./api/diagnostics";
 export type * from "./api/diagnostics";
 export { DIAGNOSTICS_EVENTS_PATH } from "./api/diagnostics";
@@ -80,6 +82,7 @@ export const api = {
   ...adminApi,
   ...plexApi,
   ...downloadsApi,
+  ...filesApi,
   ...diagnosticsApi,
   ...debugSessionsApi,
 };