feat: add ThumbnailStrip filmstrip component

apps/web/src/components/common/thumbnail-strip.tsx

@@ -0,0 +1,57 @@
+import { useRef, useEffect } from "react";
+import { CheckCircle2, XCircle } from "lucide-react";
+import type { FileEntry } from "@/stores/file-store";
+
+interface ThumbnailStripProps {
+  entries: FileEntry[];
+  selectedIndex: number;
+  onSelect: (index: number) => void;
+}
+
+export function ThumbnailStrip({ entries, selectedIndex, onSelect }: ThumbnailStripProps) {
+  const selectedRef = useRef<HTMLButtonElement>(null);
+
+  useEffect(() => {
+    selectedRef.current?.scrollIntoView({
+      block: "nearest",
+      inline: "nearest",
+      behavior: "smooth",
+    });
+  }, [selectedIndex]);
+
+  if (entries.length <= 1) return null;
+
+  return (
+    <div className="flex gap-1.5 px-3 py-2 overflow-x-auto border-t border-border bg-muted/30" style={{ scrollBehavior: "smooth" }}>
+      {entries.map((entry, i) => {
+        const isSelected = i === selectedIndex;
+        const isCompleted = entry.status === "completed";
+        const isFailed = entry.status === "failed";
+        return (
+          <button
+            key={`${entry.file.name}-${i}`}
+            ref={isSelected ? selectedRef : undefined}
+            onClick={() => onSelect(i)}
+            className={`relative shrink-0 rounded overflow-hidden transition-all ${
+              isSelected ? "outline outline-2 outline-primary outline-offset-1" : "hover:outline hover:outline-1 hover:outline-border"
+            }`}
+            style={{ width: 52, height: 38 }}
+            title={entry.file.name}
+          >
+            <img src={entry.processedUrl ?? entry.blobUrl} alt={entry.file.name} className="w-full h-full object-cover" draggable={false} />
+            {isCompleted && (
+              <div className="absolute -top-0.5 -right-0.5 w-3.5 h-3.5 bg-green-500 rounded-full flex items-center justify-center">
+                <CheckCircle2 className="h-2.5 w-2.5 text-white" />
+              </div>
+            )}
+            {isFailed && (
+              <div className="absolute -top-0.5 -right-0.5 w-3.5 h-3.5 bg-red-500 rounded-full flex items-center justify-center">
+                <XCircle className="h-2.5 w-2.5 text-white" />
+              </div>
+            )}
+          </button>
+        );
+      })}
+    </div>
+  );
+}