feat(25-03): create ChatFilePreview and ChatFileCard components

- ChatFileCard: icon, filename, size, download button with theme-aware bg-muted styling
- ChatFilePreview: inline image rendering with constrained max-h-[300px], ChatFileCard for all other types
- formatFileSize helper (B, KB, MB)
- lucide icons: ImageIcon, FileCode, FileText, File per category

ui/src/components/ChatFileCard.tsx

@@ -0,0 +1,67 @@
+import { Download, File, FileCode, FileText, ImageIcon } from "lucide-react";
+import { cn } from "../lib/utils";
+import type { ChatFile } from "@paperclipai/shared";
+
+interface ChatFileCardProps {
+  file: ChatFile;
+  contentPath: string;
+  className?: string;
+}
+
+export function formatFileSize(bytes: number): string {
+  if (bytes < 1024) return `${bytes} B`;
+  if (bytes < 1024 * 1024) return `${(bytes / 1024).toFixed(1)} KB`;
+  return `${(bytes / (1024 * 1024)).toFixed(1)} MB`;
+}
+
+function FileIcon({ category }: { category: ChatFile["category"] }) {
+  const cls = "h-5 w-5 shrink-0 text-muted-foreground";
+  switch (category) {
+    case "image":
+      return <ImageIcon className={cls} />;
+    case "code":
+      return <FileCode className={cls} />;
+    case "document":
+      return <FileText className={cls} />;
+    default:
+      return <File className={cls} />;
+  }
+}
+
+export function ChatFileCard({ file, contentPath, className }: ChatFileCardProps) {
+  return (
+    <div
+      className={cn(
+        "flex items-center gap-3 rounded-lg border border-border bg-muted p-3",
+        className,
+      )}
+    >
+      <FileIcon category={file.category} />
+
+      <div className="flex min-w-0 flex-1 flex-col">
+        <span
+          className="truncate text-sm font-medium text-foreground"
+          title={file.originalFilename}
+        >
+          {file.originalFilename}
+        </span>
+        <span className="text-xs text-muted-foreground">
+          {formatFileSize(file.sizeBytes)}
+        </span>
+      </div>
+
+      <a
+        href={contentPath}
+        download={file.originalFilename}
+        target="_blank"
+        rel="noreferrer"
+        className="shrink-0 rounded p-1 text-muted-foreground transition-colors hover:text-foreground focus-visible:outline-none focus-visible:ring-1 focus-visible:ring-ring"
+        aria-label={`Download ${file.originalFilename}`}
+        title="Download"
+        onClick={(e) => e.stopPropagation()}
+      >
+        <Download className="h-4 w-4" />
+      </a>
+    </div>
+  );
+}

ui/src/components/ChatFilePreview.tsx

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+import { ChatFileCard } from "./ChatFileCard";
+import type { ChatFile } from "@paperclipai/shared";
+
+interface ChatFilePreviewProps {
+  file: ChatFile;
+  contentPath: string;
+}
+
+export function ChatFilePreview({ file, contentPath }: ChatFilePreviewProps) {
+  if (file.category === "image") {
+    return (
+      <div className="flex flex-col gap-1">
+        <a href={contentPath} target="_blank" rel="noreferrer" className="block w-fit">
+          <img
+            src={contentPath}
+            alt={file.originalFilename}
+            loading="lazy"
+            className="max-h-[300px] rounded-lg object-contain"
+          />
+        </a>
+        {/* Always show card below image for download button */}
+        <ChatFileCard file={file} contentPath={contentPath} />
+      </div>
+    );
+  }
+
+  // For all non-image types (code, document, other): render the file card with download
+  return <ChatFileCard file={file} contentPath={contentPath} />;
+}