fix(analytics): omit empty workspace_id/workflow_id on copilot_chat_sent

Final-sweep nit: copilot_chat_sent sent '' for workspace_id/workflow_id in the
agent (workspace-less) branch, same phantom-bucket issue as file_downloaded.
Make both properties optional and omit them when absent.

Author: waleedlatif1

apps/sim/lib/copilot/chat/post.ts

@@ -1081,8 +1081,8 @@ export async function handleUnifiedChatPost(req: NextRequest) {
         authenticatedUserId,
         'copilot_chat_sent',
         {
-          workflow_id: branch.kind === 'workflow' ? branch.workflowId : '',
-          workspace_id: workspaceId ?? '',
+          ...(branch.kind === 'workflow' ? { workflow_id: branch.workflowId } : {}),
+          ...(workspaceId ? { workspace_id: workspaceId } : {}),
           has_file_attachments: (body.fileAttachments?.length ?? 0) > 0,
           has_contexts: normalizedContexts.length > 0,
           mode: branch.kind === 'workflow' ? branch.mode : 'agent',

apps/sim/lib/posthog/events.ts

@@ -360,8 +360,8 @@ export interface PostHogEventMap {
   }
 
   copilot_chat_sent: {
-    workflow_id: string
-    workspace_id: string
+    workflow_id?: string
+    workspace_id?: string
     has_file_attachments: boolean
     has_contexts: boolean
     mode: string