feat(downloads): public generic-file watch surface (E7 S5d)

The /watch/{token} SPA gets a third branch: media_kind==='file' renders an
info card (name / TYPE · size) + a Download button, no player. The <video>/
<audio> branches now guard on media_kind!=='file' so legacy links
(media_kind null) still play. Download is gated on the link's allow_download,
mirroring the media branch; the backend serves a file force-download
(attachment + octet-stream) regardless, so the gate only reflects owner ACL.

FE-only (public_meta already emits media_kind/size_bytes/container since S5a).
i18n HU/EN/DE 'file' fallback label. Two DOM tests: file -> info card +
Download, no player; view-only file -> no Download.

frontend/src/components/WatchPage.dom.test.tsx

@@ -36,4 +36,41 @@ describe("WatchPage media element (S3 · 5a)", () => {
     await waitFor(() => expect(container.querySelector("video")).not.toBeNull());
     expect(container.querySelector("audio")).toBeNull();
   });
+
+  it("renders an info card + Download for a generic file, no player (S5d)", async () => {
+    window.history.replaceState({}, "", "/watch/tok-file");
+    mockMeta({
+      needs_password: false,
+      media_kind: "file",
+      title: "report.pdf",
+      container: "pdf",
+      size_bytes: 2_400_000,
+      allow_download: true,
+      file_url: "/f.pdf",
+    });
+    const { container, findByText } = render(<WatchPage />);
+    await findByText("report.pdf");
+    expect(container.querySelector("video")).toBeNull();
+    expect(container.querySelector("audio")).toBeNull();
+    // Type · size chip and a Download link to the file.
+    await findByText(/PDF · 2\.3 MB/);
+    const dl = container.querySelector('a[href="/f.pdf"]');
+    expect(dl).not.toBeNull();
+  });
+
+  it("omits the Download for a view-only file link (S5d)", async () => {
+    window.history.replaceState({}, "", "/watch/tok-file-noview");
+    mockMeta({
+      needs_password: false,
+      media_kind: "file",
+      title: "secret.zip",
+      container: "zip",
+      size_bytes: 1000,
+      allow_download: false,
+      file_url: "/f.zip",
+    });
+    const { container, findByText } = render(<WatchPage />);
+    await findByText("secret.zip");
+    expect(container.querySelector('a[href="/f.zip"]')).toBeNull();
+  });
 });

frontend/src/components/WatchPage.tsx

@@ -1,6 +1,7 @@
 import { useEffect, useRef, useState } from "react";
-import { Download, Link2, Lock, PlayCircle } from "lucide-react";
+import { Download, File as FileIcon, Link2, Lock, PlayCircle } from "lucide-react";
 import { Button } from "./ui/Button";
+import { formatBytes } from "../lib/format";
 
 // Standalone, login-free video page for a shared /watch/<token> link. Rendered OUTSIDE the app
 // tree (no auth, no providers) — like the /privacy and /terms pages. Uses plain fetch and a tiny
@@ -48,6 +49,9 @@ type Meta = {
   extra_links?: string[];
   duration_s?: number | null;
   audio?: boolean;
+  media_kind?: "video" | "audio" | "file" | null;
+  size_bytes?: number | null;
+  container?: string | null;
   allow_download?: boolean;
   file_url?: string;
   poster_url?: string | null;
@@ -73,6 +77,7 @@ const STR = {
     watch: "Watch",
     wrong: "Wrong password.",
     download: "Download",
+    file: "File",
     links: "Links",
     brand: "Shared via Siftlode",
   },
@@ -85,6 +90,7 @@ const STR = {
     watch: "Megnézem",
     wrong: "Hibás jelszó.",
     download: "Letöltés",
+    file: "Fájl",
     links: "Linkek",
     brand: "Megosztva a Siftlode-dal",
   },
@@ -97,6 +103,7 @@ const STR = {
     watch: "Ansehen",
     wrong: "Falsches Passwort.",
     download: "Herunterladen",
+    file: "Datei",
     links: "Links",
     brand: "Geteilt über Siftlode",
   },
@@ -215,7 +222,37 @@ export default function WatchPage() {
           </div>
         )}
 
-        {status === "ready" && meta && (
+        {status === "ready" && meta && meta.media_kind === "file" && (
+          /* A generic uploaded file has no player — just an info card (name/type/size) and, if the
+             link allows it, a Download. The backend serves the file force-download regardless, so
+             gating the button on allow_download only mirrors the owner's ACL, matching the media
+             branch's download affordance below. */
+          <div className="flex-1 grid place-items-center">
+            <div className="w-full max-w-md rounded-2xl glass p-6 text-center">
+              <div className="mx-auto w-16 h-16 rounded-xl bg-surface grid place-items-center mb-4">
+                <FileIcon className="w-8 h-8 text-accent" />
+              </div>
+              <h1 className="text-lg font-semibold leading-snug break-words">
+                {meta.title || T.file}
+              </h1>
+              <div className="text-sm text-muted mt-1">
+                {[meta.container?.toUpperCase(), formatBytes(meta.size_bytes)]
+                  .filter(Boolean)
+                  .join(" · ")}
+              </div>
+              {meta.allow_download && (
+                <a
+                  href={meta.file_url}
+                  className="mt-5 inline-flex items-center gap-1.5 rounded-lg bg-surface hover:bg-card px-4 py-2 text-sm font-medium transition"
+                >
+                  <Download className="w-4 h-4" /> {T.download}
+                </a>
+              )}
+            </div>
+          </div>
+        )}
+
+        {status === "ready" && meta && meta.media_kind !== "file" && (
           <div>
             {meta.audio ? (
               /* Audio-only asset (mp3): WebKit won't play it in a <video>, so render a native