feat: add deprecation warnings for Claude Code SDK to Claude Agent SDK migration

Add DeprecationWarning to both ClaudeSDKClient and query() entry points to inform users that the package has been renamed to claude-agent-sdk and provide migration guidance.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: ashwin-ant

src/claude_code_sdk/client.py

@@ -2,6 +2,7 @@
 
 import json
 import os
+import warnings
 from collections.abc import AsyncIterable, AsyncIterator
 from dataclasses import replace
 from typing import Any
@@ -53,6 +54,14 @@ class ClaudeSDKClient:
 
     def __init__(self, options: ClaudeCodeOptions | None = None):
         """Initialize Claude SDK client."""
+        warnings.warn(
+            "The Claude Code SDK is now the Claude Agent SDK! "
+            "Please install and use claude-agent-sdk instead. "
+            "See https://docs.claude.com/en/docs/claude-code/sdk/migration-guide for migration instructions.",
+            DeprecationWarning,
+            stacklevel=2,
+        )
+
         if options is None:
             options = ClaudeCodeOptions()
         self.options = options

src/claude_code_sdk/query.py

@@ -1,6 +1,7 @@
 """Query function for one-shot interactions with Claude Code."""
 
 import os
+import warnings
 from collections.abc import AsyncIterable, AsyncIterator
 from typing import Any
 
@@ -113,6 +114,14 @@ class MyCustomTransport(Transport):
         ```
 
     """
+    warnings.warn(
+        "The Claude Code SDK is now the Claude Agent SDK! "
+        "Please install and use claude-agent-sdk instead. "
+        "See https://docs.claude.com/en/docs/claude-code/sdk/migration-guide for migration instructions.",
+        DeprecationWarning,
+        stacklevel=2,
+    )
+
     if options is None:
         options = ClaudeCodeOptions()