fix(files): a file is added when it is done, not when it was asked for

A download that failed for days and then went through sat days down the library, under its
request date, and read as missing. A job now records when it became done (`ready_at`), stamped
where the expiry already is (`folders.stamp_done`, `finalize_if_running`) and on an insert that is
already done; a check constraint holds every path to done to it. The library sorts and dates its
"Added" by it; the queue keeps the request order.

The migration dates a file from before by its "ready to watch" notice where the inbox still holds
one, else by its request date, where it already sat.

frontend/src/components/Files.menu.dom.test.tsx

@@ -11,6 +11,7 @@ import { afterEach, describe, expect, it, vi } from "vitest";
 import { act, cleanup, fireEvent, render, screen, waitFor } from "@testing-library/react";
 import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
 import { api, type FileFolder, type LibraryFile } from "../lib/api";
+import { formatDateTime } from "../lib/format";
 import {
   ALL_FILES,
   FilesActionsContext,
@@ -496,6 +497,32 @@ describe("Files · the view", () => {
     expect(screen.queryByText("Más")).not.toBeNull();
     expect(screen.queryByText("Harmadik")).toBeNull();
   });
+
+  it("dates and sorts a file by when it was done, not when it was asked for", () => {
+    // Done in another order than asked: a download that failed for days and then went through is new.
+    mocks.files = [
+      file(2, { created_at: "2026-10-01T10:00:00Z", ready_at: "2026-10-05T10:00:00Z" }),
+      file(3, { created_at: "2026-10-02T10:00:00Z", ready_at: "2026-10-12T10:00:00Z" }),
+      file(4, { created_at: "2026-10-03T10:00:00Z", ready_at: "2026-10-03T10:00:00Z" }),
+    ];
+    mocks.folders = [YT];
+    mount();
+    const order = () =>
+      [...document.querySelectorAll<HTMLElement>("[data-nav-index]")].map(
+        (r) => r.textContent?.match(/Clip \d/)?.[0],
+      );
+    const byDone = [
+      ["Clip 4", "Clip 2", "Clip 3"],
+      ["Clip 3", "Clip 2", "Clip 4"],
+    ];
+    fireEvent.click(screen.getByRole("button", { name: /files\.columns\.added/ }));
+    expect(byDone).toContainEqual(order());
+    fireEvent.click(screen.getByRole("button", { name: /files\.columns\.added/ }));
+    expect(byDone).toContainEqual(order());
+    expect(
+      rowOf("Clip 3").querySelector(`[title="${formatDateTime("2026-10-12T10:00:00Z", "en")}"]`),
+    ).not.toBeNull();
+  });
 });
 
 describe("Files · the grid", () => {

frontend/src/components/Files.tsx

@@ -402,9 +402,9 @@ export default function Files() {
       align: "right",
       nowrap: true,
       sortable: true,
-      sortValue: (f) => f.shared_at ?? f.created_at ?? "",
+      sortValue: (f) => f.shared_at ?? f.ready_at ?? f.created_at ?? "",
       render: (f) => {
-        const at = f.shared_at ?? f.created_at;
+        const at = f.shared_at ?? f.ready_at ?? f.created_at;
         return (
           <span className="text-xs text-muted" title={formatDateTime(at, lang)}>
             {relativeTime(at, lang, t)}

frontend/src/lib/api/downloads.ts

@@ -94,7 +94,8 @@ export interface DownloadJob {
   error_code: string | null; // failure category, see backend downloads.errors.classify
   error_detail: string | null; // host-specific failure-catalog entry, see downloads.errors.diagnose
   queue_pos: number;
-  created_at: string | null;
+  created_at: string | null; // when it was asked for
+  ready_at?: string | null; // when it became done — the library's "Added"
   source_kind: string;
   source_ref: string;
   source_url: string | null; // clean "downloaded from" URL (null for edit clips)