feat(rt-import): add Image to Base64 converter utility

New drag-and-drop section at the bottom of the Import RT page so operators
can convert screenshots to base64 without leaving the page. Includes
thumbnail preview, copy-base64 and copy-JSON-snippet buttons with
2s feedback, per-image delete and clear-all.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/pages/ImportRTPage.tsx

@@ -1,4 +1,4 @@
-import { useState, useRef } from "react";
+import { useState, useRef, useCallback } from "react";
 import { useMutation } from "@tanstack/react-query";
 import {
   Upload,
@@ -10,6 +10,11 @@ import {
   Loader2,
   ChevronDown,
   ChevronUp,
+  ImageIcon,
+  Copy,
+  Check,
+  Trash2,
+  Braces,
 } from "lucide-react";
 import { importRT, type RTImportPayload, type RTTechniqueEntry, type RTEvidenceEntry } from "../api/tests";
 
@@ -438,6 +443,188 @@ export default function ImportRTPage() {
           {(importMutation.error as Error)?.message || "Import failed"}
         </div>
       )}
+
+      {/* ── Base64 Image Converter ─────────────────────────────────── */}
+      <Base64Converter />
+    </div>
+  );
+}
+
+/* ── Base64 Converter Component ────────────────────────────────────── */
+
+interface ConvertedImage {
+  id: string;
+  filename: string;
+  dataUrl: string;   // data:image/xxx;base64,... — used for <img> preview
+  b64: string;       // raw base64 data — used in the JSON evidence field
+  sizeKb: number;
+}
+
+function Base64Converter() {
+  const [images, setImages] = useState<ConvertedImage[]>([]);
+  const [dragging, setDragging] = useState(false);
+  const [copiedId, setCopiedId] = useState<string | null>(null);
+  const inputRef = useRef<HTMLInputElement>(null);
+
+  const processFiles = useCallback((files: FileList | File[]) => {
+    const fileArr = Array.from(files);
+    const allowed = ["image/png", "image/jpeg", "image/gif", "image/webp", "image/bmp"];
+    fileArr.forEach((file) => {
+      if (!allowed.includes(file.type)) return;
+      const reader = new FileReader();
+      reader.onload = (e) => {
+        const dataUrl = e.target?.result as string;
+        // dataUrl = "data:image/png;base64,iVBORw..."
+        const b64 = dataUrl.split(",")[1] ?? "";
+        setImages((prev) => [
+          ...prev,
+          {
+            id: crypto.randomUUID(),
+            filename: file.name,
+            dataUrl,
+            b64,
+            sizeKb: Math.round(file.size / 1024),
+          },
+        ]);
+      };
+      reader.readAsDataURL(file);
+    });
+  }, []);
+
+  const handleDrop = useCallback(
+    (e: React.DragEvent) => {
+      e.preventDefault();
+      setDragging(false);
+      if (e.dataTransfer.files.length) processFiles(e.dataTransfer.files);
+    },
+    [processFiles],
+  );
+
+  const copyToClipboard = (text: string, id: string) => {
+    navigator.clipboard.writeText(text).then(() => {
+      setCopiedId(id);
+      setTimeout(() => setCopiedId(null), 2000);
+    });
+  };
+
+  const jsonSnippet = (img: ConvertedImage) =>
+    JSON.stringify({ filename: img.filename, data: img.b64, caption: "" }, null, 2);
+
+  return (
+    <div className="rounded-xl border border-purple-500/20 bg-gray-900 p-5 space-y-4">
+      {/* Header */}
+      <div className="flex items-center justify-between">
+        <div className="flex items-center gap-2">
+          <div className="rounded-lg bg-purple-500/10 p-1.5">
+            <ImageIcon className="h-4 w-4 text-purple-400" />
+          </div>
+          <div>
+            <h2 className="text-sm font-semibold text-white">Image → Base64 Converter</h2>
+            <p className="text-xs text-gray-500">
+              Drop screenshots here to get their base64 — paste directly into your JSON
+            </p>
+          </div>
+        </div>
+        {images.length > 0 && (
+          <button
+            onClick={() => setImages([])}
+            className="flex items-center gap-1.5 rounded-lg border border-gray-700 px-2.5 py-1.5 text-xs text-gray-400 hover:border-red-500/40 hover:text-red-400 transition-colors"
+          >
+            <Trash2 className="h-3 w-3" />
+            Clear all
+          </button>
+        )}
+      </div>
+
+      {/* Drop zone */}
+      <div
+        onDragOver={(e) => { e.preventDefault(); setDragging(true); }}
+        onDragLeave={() => setDragging(false)}
+        onDrop={handleDrop}
+        onClick={() => inputRef.current?.click()}
+        className={`flex cursor-pointer flex-col items-center justify-center gap-2 rounded-xl border-2 border-dashed py-8 transition-colors ${
+          dragging
+            ? "border-purple-400 bg-purple-500/10"
+            : "border-gray-700 hover:border-purple-500/50 hover:bg-purple-500/5"
+        }`}
+      >
+        <Upload className={`h-6 w-6 transition-colors ${dragging ? "text-purple-400" : "text-gray-600"}`} />
+        <p className="text-sm text-gray-500">
+          <span className="font-medium text-purple-400">Click or drag</span> images here
+        </p>
+        <p className="text-xs text-gray-600">PNG · JPG · GIF · WebP · BMP</p>
+        <input
+          ref={inputRef}
+          type="file"
+          accept="image/png,image/jpeg,image/gif,image/webp,image/bmp"
+          multiple
+          className="hidden"
+          onChange={(e) => { if (e.target.files) { processFiles(e.target.files); e.target.value = ""; } }}
+        />
+      </div>
+
+      {/* Converted images */}
+      {images.length > 0 && (
+        <div className="space-y-3">
+          {images.map((img) => (
+            <div key={img.id} className="flex gap-3 rounded-xl border border-gray-800 bg-gray-800/40 p-3">
+              {/* Thumbnail */}
+              <img
+                src={img.dataUrl}
+                alt={img.filename}
+                className="h-20 w-20 shrink-0 rounded-lg border border-gray-700 object-cover"
+              />
+
+              {/* Info + actions */}
+              <div className="flex flex-1 flex-col gap-2 min-w-0">
+                <div className="flex items-center justify-between gap-2">
+                  <p className="truncate text-sm font-medium text-gray-200">{img.filename}</p>
+                  <span className="shrink-0 text-xs text-gray-500">{img.sizeKb} KB</span>
+                </div>
+
+                {/* base64 preview (truncated) */}
+                <div className="rounded-lg border border-gray-700 bg-gray-900 px-3 py-1.5">
+                  <p className="truncate font-mono text-xs text-gray-500">
+                    {img.b64.slice(0, 80)}…
+                  </p>
+                </div>
+
+                {/* Copy buttons */}
+                <div className="flex gap-2">
+                  <button
+                    onClick={() => copyToClipboard(img.b64, `b64-${img.id}`)}
+                    className="flex items-center gap-1.5 rounded-lg border border-gray-700 bg-gray-800 px-3 py-1.5 text-xs font-medium text-gray-300 hover:border-cyan-500/40 hover:text-cyan-400 transition-colors"
+                  >
+                    {copiedId === `b64-${img.id}` ? (
+                      <><Check className="h-3 w-3 text-green-400" /><span className="text-green-400">Copied!</span></>
+                    ) : (
+                      <><Copy className="h-3 w-3" />Copy base64</>
+                    )}
+                  </button>
+
+                  <button
+                    onClick={() => copyToClipboard(jsonSnippet(img), `json-${img.id}`)}
+                    className="flex items-center gap-1.5 rounded-lg border border-gray-700 bg-gray-800 px-3 py-1.5 text-xs font-medium text-gray-300 hover:border-purple-500/40 hover:text-purple-400 transition-colors"
+                  >
+                    {copiedId === `json-${img.id}` ? (
+                      <><Check className="h-3 w-3 text-green-400" /><span className="text-green-400">Copied!</span></>
+                    ) : (
+                      <><Braces className="h-3 w-3" />Copy JSON snippet</>
+                    )}
+                  </button>
+
+                  <button
+                    onClick={() => setImages((prev) => prev.filter((im) => im.id !== img.id))}
+                    className="ml-auto rounded-lg border border-gray-700 p-1.5 text-gray-600 hover:border-red-500/40 hover:text-red-400 transition-colors"
+                  >
+                    <Trash2 className="h-3 w-3" />
+                  </button>
+                </div>
+              </div>
+            </div>
+          ))}
+        </div>
+      )}
     </div>
   );
 }