Fix: Correct streamChunk content access in README example

Problem

The README example incorrectly uses streamChunk.content, but the actual response structure requires streamChunk.choices[0].message.content to access the message content.

Solution

Updated the README example to use the correct API response structure:

• Changed from: streamChunk.content
• Changed to: streamChunk.choices[0].message.content

Verification

1. StreamChunk Interface Definition

Location: src/resources/chat/chat.ts

export interface StreamChunk {
  id: string;
  choices: Array<Shared.Choice>;  // ✅ Has 'choices' property
  created: number;
  model: string;
  // ... other properties
  // ❌ Does NOT have 'content' property
}

2. Choice Interface Definition

Location: src/resources/shared.ts

export interface Choice {
  delta: ChatMessageOutput;
  index: number;
  message: ChatMessageOutput;  // ✅ Has 'message' property
  finish_reason?: 'stop' | 'length' | null;
}

3. ChatMessageOutput Interface Definition

Location: src/resources/shared.ts

export interface ChatMessageOutput {
  content: string | Array<...> | null;  // ✅ Has 'content' property
  role: 'system' | 'user' | 'assistant' | 'tool';
  // ... other properties
}

4. Correct Access Path

StreamChunk
  └── choices: Array<Choice>
        └── [0] (first Choice)
              └── message: ChatMessageOutput
                    └── content: string | Array<...> | null

Correct usage:

streamChunk.choices[0].message.content

Impact

This change ensures developers can properly access the message content from chat completions without encountering runtime errors.