perf(fs): 1MiB stream chunks, full sha256 via sha256sum subprocess, walk cap

- copy streams use 1MiB highWaterMark
- forced full sha256 uses Deno.Command(sha256sum), falls back to in-process stream;
  method recorded as hashVia and counted
- per-file organize.transfer timing log
- ORGANIZE_WALK_MAX_FILES caps manual path walks; dryRun returns truncated

Co-Authored-By: Claude Opus 5.5 <[email protected]>

apps/web/app/components/downloads/organize-dialog.tsx

@@ -162,8 +162,13 @@ export function OrganizeDialog({
     setErrors({});
     organize.mutate(parsed.data, {
       onSuccess: (r) => {
-        if (dryRun) setPlanId(r.planId);
-        else {
+        if (dryRun) {
+          setPlanId(r.planId);
+          if (r.truncated)
+            toast.warning("源目录文件数超过上限,预览只含前一部分文件", {
+              description: "正式执行会被拒绝,请把源路径缩小到具体的作品目录",
+            });
+        } else {
           toast.success("已发起整理");
           onOpenChange(false);
           if (r.recordId) navigate(`/console/organize/${r.recordId}`);