fix: Import A2A well known path from A2A sdk

PiperOrigin-RevId: 783036797

contributing/samples/a2a_basic/agent.py

@@ -15,6 +15,7 @@
 import random
 
 from google.adk.agents import Agent
+from google.adk.agents.remote_a2a_agent import AGENT_CARD_WELL_KNOWN_PATH
 from google.adk.agents.remote_a2a_agent import RemoteA2aAgent
 from google.adk.tools.example_tool import ExampleTool
 from google.genai import types
@@ -87,7 +88,7 @@ prime_agent = RemoteA2aAgent(
     name="prime_agent",
     description="Agent that handles checking if numbers are prime.",
     agent_card=(
-        "http://localhost:8001/a2a/check_prime_agent/.well-known/agent.json"
+        f"http://localhost:8001/a2a/check_prime_agent{AGENT_CARD_WELL_KNOWN_PATH}"
     ),
 )