feat(files): share a folder by link — its page lists what is in it, plays a video above the list

A /watch link may now open one of its owner's own folders (migration 0108: folder_id beside job_id,
exactly one set; a folder's links go with it). The page shows what is in the folder when it is
opened, newest first: a video or a song plays in the same player a file link has, above the list,
each keeping its own resume point; a document only downloads, never opens as a page. A file moved
out stops opening through the link at its next request. Password, expiry and stream-only work as on
a file link; the unfurl names the folder and counts its files, never their names. Source folders
and the Hub cannot be shared.

The folder menu gets "Copy link" and "Share with a link…" (the Share dialog's link half); the rail
marks a folder a live link opens.

Two fixes in the Share dialog on the way: revoking the last link no longer mints a new one at once,
and the new-link form goes back to downloadable after making a link.

frontend/src/components/FilesRail.tsx

@@ -3,7 +3,7 @@ import { Meter } from "./ui/Meter";
 import { useQuery } from "@tanstack/react-query";
 import { useTranslation } from "react-i18next";
 import clsx from "clsx";
-import { FolderOpen, FolderPlus, HardDrive, Users } from "lucide-react";
+import { FolderOpen, FolderPlus, HardDrive, Link2, Users } from "lucide-react";
 import { api, type FileFolder } from "../lib/api";
 import { compareText } from "../lib/collate";
 import { formatBytes } from "../lib/format";
@@ -36,16 +36,20 @@ function Entry({
   view,
   trigger,
   folderId,
+  shared = false,
 }: {
   icon: React.ComponentType<{ className?: string }>;
   label: string;
   count?: number;
+  /** A live public link opens the folder: what is moved in is shown to whoever holds the link. */
+  shared?: boolean;
   view: FilesView;
   /** The folder's menu triggers (right click, long press, Shift+F10). */
   trigger?: Record<string, unknown>;
   /** A folder's entry is found by it, to hand the keyboard back after a rename. */
   folderId?: number;
 }) {
+  const { t } = useTranslation();
   const { view: current } = useFiles();
   const { setView } = useFilesActions();
   const active = sameView(view, current);
@@ -64,6 +68,12 @@ function Entry({
     >
       <Icon className={clsx("size-4 shrink-0", !active && "text-muted")} />
       <span className="min-w-0 flex-1 truncate text-left">{label}</span>
+      {shared && (
+        <span title={t("files.folder.shared")} className="shrink-0">
+          <Link2 aria-hidden className="size-3.5 text-accent" />
+          <span className="sr-only">{t("files.folder.shared")}</span>
+        </span>
+      )}
       {count !== undefined && <span className="text-xs tabular-nums text-muted">{count}</span>}
     </Pressable>
   );
@@ -176,6 +186,7 @@ export default function FilesRail({
         icon={folderIcon(f)}
         label={folderLabel(f, t)}
         count={f.count}
+        shared={f.has_link}
         view={{ kind: "folder", id: f.id }}
         trigger={menu.triggerProps(f)}
         folderId={f.id}
@@ -267,6 +278,7 @@ export default function FilesRail({
         ariaLabel={t("files.folder.menu")}
         items={menu.target ? folderActions.items(menu.target) : []}
       />
+      {folderActions.dialog}
     </FilterRail>
   );
 }