Add chat export functionality (#64)

# Add chat export functionality

## ♻️ Current situation & Problem
Without a chat export feature, users cannot save or reference their
conversation history, leading to lost information and manual
copy-pasting workarounds.

## ⚙️ Release Notes 
Added a feature to export chat conversations in text format.


## 📚 Documentation
N/A


## ✅ Testing
N/A


### Code of Conduct & Contributing Guidelines 

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of
Conduct](https://github.com/StanfordBDHG/.github/blob/main/CODE_OF_CONDUCT.md)
and [Contributing
Guidelines](https://github.com/StanfordBDHG/.github/blob/main/CONTRIBUTING.md):
- [x] I agree to follow the [Code of
Conduct](https://github.com/StanfordBDHG/.github/blob/main/CODE_OF_CONDUCT.md)
and [Contributing
Guidelines](https://github.com/StanfordBDHG/.github/blob/main/CONTRIBUTING.md).

LLMonFHIR/FHIRInterpretation/MultipleResources/MultipleResourcesChatView.swift

@@ -42,6 +42,7 @@ struct MultipleResourcesChatView: View {
                     set: { llm.context.chat = $0 }
                 ),
                 disableInput: llm.state.representation == .processing,
+                exportFormat: .text,
                 messagePendingAnimation: .automatic
             )
             .speak(llm.context.chat, muted: !textToSpeech)