feat(downloads): share UI — user picker + public watch links + watch page

Rework the share dialog into two clear modes and add the public /watch player page:
- ShareDialog: (A) 'Share with a user' — autocomplete picker over registered users (was a blind
  email box that 404'd on non-users); (B) 'Share a link' — create/list/copy/revoke public links
  with allow-download toggle, optional expiry (1/7/30d), optional password; per-link view count.
- WatchPage: standalone login-free player at /watch/<token> (routed in main.tsx like /privacy),
  self-contained mini-i18n (en/hu/de by browser language); password gate → unlock → play; shows a
  Download button only when the link allows it.
- api: ShareLink/ShareRecipient types + link CRUD + recipients; share i18n (en/hu/de).
Verified end-to-end in a real browser: user picker, link create, public playback, stream-only vs
downloadable, password gate + unlock, no console errors.

frontend/src/components/DownloadCenter.tsx

@@ -19,6 +19,7 @@ import Modal from "./Modal";
 import DownloadDialog from "./DownloadDialog";
 import ProfileEditor from "./ProfileEditor";
 import VideoEditor from "./VideoEditor";
+import ShareDialog from "./ShareDialog";
 import { useConfirm } from "./ConfirmProvider";
 import { useLiveQuery } from "../lib/useLiveQuery";
 import { api, type DownloadJob, type Me } from "../lib/api";
@@ -186,39 +187,6 @@ function RenameModal({ job, onClose }: { job: DownloadJob; onClose: () => void }
   );
 }
 
-function ShareModal({ job, onClose }: { job: DownloadJob; onClose: () => void }) {
-  const { t } = useTranslation();
-  const [email, setEmail] = useState("");
-  const share = useMutation({
-    mutationFn: () => api.shareDownload(job.id, email.trim()),
-    onSuccess: (r) => {
-      notify({ level: "success", message: t("downloads.share.done", { email: r.shared_with }) });
-      onClose();
-    },
-  });
-  return (
-    <Modal title={t("downloads.share.title")} onClose={onClose}>
-      <label className="block text-sm font-medium mb-1">{t("downloads.share.label")}</label>
-      <input
-        value={email}
-        onChange={(e) => setEmail(e.target.value)}
-        placeholder={t("downloads.share.placeholder")}
-        className={inputCls}
-        autoFocus
-      />
-      <div className="flex justify-end mt-4">
-        <button
-          onClick={() => share.mutate()}
-          disabled={!email.trim() || share.isPending}
-          className="px-3 py-1.5 rounded-lg text-sm font-medium bg-accent text-accent-fg hover:opacity-90 disabled:opacity-50 transition"
-        >
-          {t("downloads.share.submit")}
-        </button>
-      </div>
-    </Modal>
-  );
-}
-
 // --- Usage bar ------------------------------------------------------------------------------
 
 function UsageBar() {
@@ -541,7 +509,7 @@ export default function DownloadCenter({ me }: { me: Me }) {
       )}
       {manage && <ProfileEditor onClose={() => setManage(false)} />}
       {renameJob && <RenameModal job={renameJob} onClose={() => setRenameJob(null)} />}
-      {shareJob && <ShareModal job={shareJob} onClose={() => setShareJob(null)} />}
+      {shareJob && <ShareDialog job={shareJob} onClose={() => setShareJob(null)} />}
       {editJob && <VideoEditor job={editJob} onClose={() => setEditJob(null)} />}
     </div>
   );