fix(downloads): media-library UI review fixes (E7)

Deep-review remediation on the frontend, all findings adversarially verified:

- LibraryPlayer picks audio vs video from the canonical media_kind (single source), not a
  hardcoded container whitelist, so an uploaded audio file with an uncommon/absent container
  renders in <audio> instead of a broken video box (legacy null media_kind keeps the heuristic).
- UploadDialog aborts the in-flight upload when the dialog is closed by X/ESC/backdrop/Back
  (not only the footer Cancel); drag highlight uses an enter/leave depth counter to stop the
  flicker; the progress bar gets a stable role=progressbar aria-label with the value on aria-valuenow.
- DownloadCenter's Shared tab renders honest loading/error states instead of a blank panel, and
  the library/shared row-action gating moves to a single tested helper (lib/downloadActions).

Tests: downloadActions gating matrix, the uploadReq XHR path (abort/401/422-localize/onerror),
and the media_kind-driven audio/video branch.

i18n: downloads.upload.uploadProgress (HU + EN).

frontend/src/lib/downloadActions.test.ts

@@ -0,0 +1,79 @@
+// E7·S5b — the Library/Shared row-action gate. A generic uploaded file (media_kind='file') is
+// download+share only (no Play/Edit/Details); an edit clip and an upload can't be re-downloaded.
+// These pin the gate so a regression that shows Play/Edit on a file, or re-download on an upload,
+// is caught (the affordance itself, not just the backend guard behind it).
+import { describe, it, expect } from "vitest";
+import { libraryRowActions, sharedRowActions } from "./downloadActions";
+import type { DownloadJob } from "./api";
+
+const job = (
+  over: Partial<DownloadJob>,
+  asset: Partial<NonNullable<DownloadJob["asset"]>> | null,
+) =>
+  ({
+    id: 1,
+    status: "done",
+    job_kind: "download",
+    can_download: true,
+    asset: asset && {
+      id: 1,
+      status: "ready",
+      title: "x",
+      duration_s: 90,
+      media_kind: "video",
+      container: "mp4",
+      ...asset,
+    },
+    ...over,
+  }) as unknown as DownloadJob;
+
+describe("libraryRowActions", () => {
+  it("a media (video) item gets play, edit, details, redownload", () => {
+    expect(libraryRowActions(job({}, {}))).toEqual({
+      play: true,
+      edit: true,
+      editDetails: true,
+      redownload: true,
+    });
+  });
+
+  it("a generic file gets NO play/edit/details (download+share only)", () => {
+    const a = libraryRowActions(job({}, { media_kind: "file", duration_s: null }));
+    expect(a.play).toBe(false);
+    expect(a.edit).toBe(false);
+    expect(a.editDetails).toBe(false);
+  });
+
+  it("an upload cannot be re-downloaded (no re-fetchable source)", () => {
+    expect(libraryRowActions(job({ job_kind: "upload" }, { media_kind: "file" })).redownload).toBe(
+      false,
+    );
+  });
+
+  it("an edit clip cannot be re-downloaded", () => {
+    expect(libraryRowActions(job({ job_kind: "edit" }, {})).redownload).toBe(false);
+  });
+
+  it("edit is hidden when the media has no duration", () => {
+    expect(libraryRowActions(job({}, { duration_s: 0 })).edit).toBe(false);
+  });
+});
+
+describe("sharedRowActions", () => {
+  it("a downloadable media item gets play, save, edit", () => {
+    expect(sharedRowActions(job({}, {}))).toEqual({ play: true, save: true, edit: true });
+  });
+
+  it("nothing is offered when the owner disabled download", () => {
+    expect(sharedRowActions(job({ can_download: false }, {}))).toEqual({
+      play: false,
+      save: false,
+      edit: false,
+    });
+  });
+
+  it("a shared generic file gets only save (no player/trim)", () => {
+    const a = sharedRowActions(job({}, { media_kind: "file", duration_s: null }));
+    expect(a).toEqual({ play: false, save: true, edit: false });
+  });
+});