fix: update all test mocks for call_llm migration

Update 14 test files to use the new call_llm/async_call_llm mock
patterns instead of the old get_text_auxiliary_client/
get_vision_auxiliary_client tuple returns.

- vision_tools tests: mock async_call_llm instead of _aux_async_client
- browser tests: mock call_llm instead of _aux_vision_client
- flush_memories tests: mock call_llm instead of get_text_auxiliary_client
- session_search tests: mock async_call_llm with RuntimeError
- mcp_tool tests: fix whitelist model config, use side_effect for
  multi-response tests
- auxiliary_config_bridge: update for model=None (resolved in router)

3251 passed, 2 pre-existing unrelated failures.

tests/test_run_agent.py

@@ -959,7 +959,7 @@ class TestFlushSentinelNotLeaked:
         agent.client.chat.completions.create.return_value = mock_response
 
         # Bypass auxiliary client so flush uses agent.client directly
-        with patch("agent.auxiliary_client.get_text_auxiliary_client", return_value=(None, None)):
+        with patch("agent.auxiliary_client.call_llm", side_effect=RuntimeError("no provider")):
             agent.flush_memories(messages, min_turns=0)
 
         # Check what was actually sent to the API