Switch cloud-upstream preview to manifest-only shape (PAP-9798)

Companies with thousands of issues serialize to >64 MiB when we ship
every entity body to the cloud preview endpoint, so the wizard cannot
leave the Connect step. The cloud now accepts a manifest-only preview
shape (PAP-9797, cloud commit 41d3551); opt into it so the Preview push
button works at PAP scale.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

server/src/services/cloud-upstreams.ts

@@ -253,9 +253,15 @@ export function cloudUpstreamService(db: Db, options: { instanceId?: string } =
       }
 
       const bundle = await buildBundle(connection, "preview");
+      const conflictKeysBySource: Record<string, string[]> = {};
+      for (const entity of bundle.entities) {
+        if (!entity.conflictKeys || entity.conflictKeys.length === 0) continue;
+        conflictKeysBySource[sourceEntityKeyString(entity.record.key)] = [...entity.conflictKeys];
+      }
       const remotePreview = await remotePost(connection, `/api/companies/${encodeURIComponent(connection.targetCompanyId)}/upstream-imports/preview`, {
         manifest: bundle.manifest,
-        entities: bundle.entities,
+        previewShape: "manifest_only",
+        conflictKeysBySource,
       });
       return {
         ...basePreview,
@@ -1059,6 +1065,12 @@ function shortHash(value: string): string {
   return crypto.createHash("sha256").update(value).digest("hex").slice(0, 12);
 }
 
+function sourceEntityKeyString(key: SourceEntityKey): string {
+  return [key.sourceInstanceId, key.sourceCompanyId, key.sourceEntityType, key.sourceEntityId]
+    .map((part) => encodeURIComponent(part))
+    .join("/");
+}
+
 function titleFromCode(code: string): string {
   return code
     .replace(/_/g, " ")