fix(files): review round 1, the page — honest states, the keyboard, the tray's words

- A library past the list's cap is searched and sorted on the server; the count says "the newest".
- Each folder and each search opens on its first page (DataTable pageScope, useCardPager scope).
- A file dropped where the page takes none never reaches the browser (which would unload the app).
- The viewer's arrows wait while a layer opened from it is on top, and scroll a wide text line;
  a text shows its first 5000 lines and says where the rest is.
- Confirms name the file (no more "your downloads"); the asking menu rows end in "…".
- The tray names a running step beside its bar, shows a pause mark for paused work, polls slowly
  while only paused work waits, and forgets a finished file that was deleted.
- An unchanged rename sends nothing; a paste opens the download dialog only with nothing on top;
  the link box never replaces what was typed.
- Honest states: folders that failed to load, a file no longer there, the storage figure; the rail
  says "nothing downloaded" only when there is nothing.
- Focus after deleting the open folder and when the format form opens; the format name's label.
- ui/Meter (one danger line for both quota bars) and ui/RenameField in the platform layer.
- Copy fixes, stale comments and the speculative hub key; a contract test for the list's
  parameters; e2e: the Files page and the paste intake.

frontend/src/lib/api/files.ts

@@ -19,7 +19,13 @@ export interface FileFolder {
   created_at: string | null;
 }
 
+// The most files one list answers with (backend `routes/files.py` MAX_LIST, held equal by
+// files.contract.test.ts): a list this long may be missing older files, so the page asks the
+// server to search and sort it rather than doing either on the rows it got.
+export const FILES_LIST_CAP = 500;
+
 export type FileSort = "added" | "name" | "size";
+export const FILE_SORTS: readonly FileSort[] = ["added", "name", "size"];
 export type FileOrder = "asc" | "desc";
 
 export interface FileListParams {
@@ -69,7 +75,8 @@ export interface StorageUsage {
   upload_max_bytes: number;
 }
 
-function listQuery(p: FileListParams): string {
+/** The list's query string — exported for the contract test that holds its names to the route's. */
+export function listQuery(p: FileListParams): string {
   const q = new URLSearchParams();
   if (p.shared) q.set("scope", "shared");
   else if (p.folderId != null) q.set("folder_id", String(p.folderId));