feat: unhide action, date-range filter, more sort options

- Hidden view shows an Unhide action (eye icon) instead of Hide
- Upload-date filter: From/To date range (inclusive); feed shows only videos
  published in that window (backend published_after / published_before)
- New sort options: Name (A-Z) and Channel subscribers, alongside date/views/
  duration/shuffle
- Native controls follow the theme via color-scheme (dark date picker)

frontend/src/components/VideoCard.tsx

@@ -1,4 +1,4 @@
-import { Bookmark, Check, EyeOff, ListFilter } from "lucide-react";
+import { Bookmark, Check, Eye, EyeOff, ListFilter } from "lucide-react";
 import clsx from "clsx";
 import type { Video } from "../lib/api";
 import { formatDuration, formatViews, relativeTime } from "../lib/format";
@@ -41,10 +41,17 @@ function Actions({
       </button>
       <button
         onClick={act("hidden")}
-        title="Hide"
-        className="p-1.5 rounded-md hover:bg-surface text-muted hover:text-fg"
+        title={video.status === "hidden" ? "Unhide" : "Hide"}
+        className={clsx(
+          "p-1.5 rounded-md hover:bg-surface text-muted hover:text-fg",
+          video.status === "hidden" && "text-accent"
+        )}
       >
-        <EyeOff className="w-4 h-4" />
+        {video.status === "hidden" ? (
+          <Eye className="w-4 h-4" />
+        ) : (
+          <EyeOff className="w-4 h-4" />
+        )}
       </button>
       {onChannelFilter && (
         <button