Python: Fix Azure AI sample errors (#4021)

* Python: Fix Azure AI sample errors

- azure_ai_with_application_endpoint: Add missing name to Agent constructor
- azure_ai_with_file_search: Fix resource path (parents[2] -> parents[3])
- azure_ai_with_openapi: Fix resource path (parents[2] -> parents[3])
- azure_ai_with_session: Use get_agent/get_session to reuse existing agent
  version and preserve conversation context across agent instances

* Python: Fix resource paths in azure_ai_agent samples

- azure_ai_with_file_search: Fix path to employees.pdf (parent.parent -> parents[3]/shared)
- azure_ai_with_openapi_tools: Fix path to weather.json/countries.json (parents[2] -> parents[3])

* fix V1 SDK hosted tools (FileSearchTool, etc.) silently dropped during agent creation

* fix: V2 file search sample uses correct SDK (AIProjectClient instead of AgentsClient)

The azure_ai/azure_ai_with_file_search.py sample incorrectly used the V1
AgentsClient for file/vector store operations. Replaced with V2 pattern:
AIProjectClient + get_openai_client() for file upload and vector store
management, matching the official Azure AI Projects SDK samples.

* fix: use context manager for file open in V2 file search sample

python/packages/azure-ai/tests/test_agent_provider.py

@@ -437,7 +437,7 @@ def test_as_agent_with_hosted_tools(
     azure_ai_unit_test_env: dict[str, str],
     mock_agents_client: MagicMock,
 ) -> None:
-    """Test as_agent handles hosted tools correctly."""
+    """Test as_agent excludes hosted tools from local tools (they stay on the server agent)."""
     mock_code_interpreter = MagicMock()
     mock_code_interpreter.type = "code_interpreter"
 
@@ -456,9 +456,10 @@ def test_as_agent_with_hosted_tools(
     agent = provider.as_agent(mock_agent)
 
     assert isinstance(agent, Agent)
-    # Should have code_interpreter dict tool in the default_options tools
+    # Hosted tools (code_interpreter, file_search, etc.) are already on the server agent
+    # and should NOT be in local tools to avoid re-sending them at run time
     tools = agent.default_options.get("tools") or []
-    assert any(isinstance(t, dict) and t.get("type") == "code_interpreter" for t in tools)
+    assert not any(isinstance(t, dict) and t.get("type") == "code_interpreter" for t in tools)
 
 
 def test_as_agent_with_dict_function_tools_validates(