refactor(ch1-4): align filenames and update corresponding README sections

m02_llm_fundamentals/s01_basic_llm_invocation.py

@@ -0,0 +1,17 @@
+from config import OPENAI_API_KEY
+from openai import OpenAI
+
+client = OpenAI(
+    api_key=OPENAI_API_KEY,
+    base_url="https://api.deepseek.com")
+
+response = client.chat.completions.create(
+    model="deepseek-chat",
+    messages=[
+        {"role": "system", "content": "You are a helpful assistant"}, # 提示词角色
+        {"role": "user", "content": "Hello"}, # 用户输入的对话
+    ],
+    stream=False # 非流式输出, 只会等语句全部生成才返回
+)
+
+print(response.choices[0].message.content)