[Bug]: Possible mismatch between texts and text_summaries in multimodal_rag_langchain.ipynb

### File Name

gemini/use-cases/retrieval-augmented-generation/multimodal_rag_langchain.ipynb

### What happened?

In the notebook `gemini/use-cases/retrieval-augmented-generation/multimodal_rag_langchain.ipynb`, there seems to be a mismatch between the IDs assigned to the original PDF chunks and the IDs used for the corresponding summaries.

The code defines:
doc_contents = texts + tables + img_base64_list

doc_ids = [str(uuid.uuid4()) for _ in doc_contents]
summary_docs = [
Document(page_content=s, metadata={id_key: doc_ids[i]})
for i, s in enumerate(text_summaries + table_summaries + image_summaries)
]

However, `texts` (from `partition_pdf`) and `text_summaries` (after an additional split via `text_splitter.split_text`) do not necessarily have the same cardinality.

### Relevant log output

```shell
Because `doc_ids` is generated from `doc_contents` and then indexed with `i` from `enumerate(text_summaries + table_summaries + image_summaries)`, any change in the number of chunks (e.g., due to re‑chunking with `text_splitter.split_text`) can shift the indices and cause summaries to be associated with the wrong original content.
```

### Code of Conduct

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