fix(docs): Custom RAG Grade Documents sample (#1155)

Corrected errors in Typescript sample for "Grade documents" section.

## Overview
Found a few issues while trying the Custom RAG sample code. Submitting a
few changes to correct the documentation.

## Type of change

**Type:** Fix typo/bug

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## Checklist
<!-- Put an 'x' in all boxes that apply -->
- [x] I have read the [contributing guidelines](README.md)
- [ ] I have tested my changes locally using `docs dev`
- [x] All code examples have been tested and work correctly
- [ ] I have used **root relative** paths for internal links
- [ ] I have updated navigation in `src/docs.json` if needed
- I have gotten approval from the relevant reviewers
- (Internal team members only / optional) I have created a preview
deployment using the [Create Preview Branch
workflow](https://github.com/langchain-ai/docs/actions/workflows/create-preview-branch.yml)

## Additional notes
<!-- Any other information that would be helpful for reviewers -->

Co-authored-by: Lauren Hirata Singh <lauren@langchain.dev>

Author: orvillem

src/oss/langgraph/agentic-rag.mdx

@@ -457,7 +457,7 @@ Note that the components will operate on the [`MessagesState`](/oss/langgraph/gr
       temperature: 0,
     }).withStructuredOutput(gradeDocumentsSchema);
 
-    const score = await chain.invoke({
+    const score = await prompt.pipe(model).invoke({
       question: messages.at(0)?.content,
       context: messages.at(-1)?.content,
     });
@@ -470,13 +470,15 @@ Note that the components will operate on the [`MessagesState`](/oss/langgraph/gr
   ```
 2. Run this with irrelevant documents in the tool response:
   ```typescript
+  import { ToolMessage } from "@langchain/core/messages";
+
   const input = {
     messages: [
         new HumanMessage("What does Lilian Weng say about types of reward hacking?"),
         new AIMessage({
             tool_calls: [
                 {
-                    type: "tool_call"
+                    type: "tool_call",
                     name: "retrieve_blog_posts",
                     args: { query: "types of reward hacking" },
                     id: "1",
@@ -499,7 +501,7 @@ Note that the components will operate on the [`MessagesState`](/oss/langgraph/gr
         new AIMessage({
             tool_calls: [
                 {
-                    type: "tool_call"
+                    type: "tool_call",
                     name: "retrieve_blog_posts",
                     args: { query: "types of reward hacking" },
                     id: "1",