fix: clean up transfer_to_agent docstring to reduce token waste

Move developer-facing note from the docstring to a code comment above
the function. The docstring is sent to the model on every tool call,
so keeping it lean reduces token usage and lowers hallucination risk.

Fixes #4615

Author: stakeswky

src/google/adk/tools/transfer_to_agent_tool.py

@@ -23,17 +23,15 @@
 from .tool_context import ToolContext
 
 
+# Note: For most use cases, you should use TransferToAgentTool instead of this
+# function directly. TransferToAgentTool provides additional enum constraints
+# that prevent LLMs from hallucinating invalid agent names.
 def transfer_to_agent(agent_name: str, tool_context: ToolContext) -> None:
   """Transfer the question to another agent.
 
   This tool hands off control to another agent when it's more suitable to
   answer the user's question according to the agent's description.
 
-  Note:
-    For most use cases, you should use TransferToAgentTool instead of this
-    function directly. TransferToAgentTool provides additional enum constraints
-    that prevent LLMs from hallucinating invalid agent names.
-
   Args:
     agent_name: the agent name to transfer to.
   """