fix(core): recover from hallucinated tool names instead of ending the scan

A tool call for a name Strix does not register raised ModelBehaviorError
from the SDK turn resolver, which nothing retries: the root agent's raise
tore down the whole scan and a sub-agent died before its status was set.
Opt into the SDK's tool_not_found_behavior="return_error_to_model" so the
unknown call comes back as a tool result and the agent self-corrects.

The setting landed in openai-agents 0.19.0, which requires openai>=2.45,
so both pins move.

strix/core/runner.py

@@ -268,6 +268,9 @@ async def run_strix_scan(
             model_settings=model_settings,
             sandbox=SandboxRunConfig(client=bundle["client"], session=bundle["session"]),
             trace_include_sensitive_data=False,
+            # A hallucinated tool name is a recoverable model mistake, not a scan-ending
+            # error: hand it back as a tool result so the agent can correct itself.
+            tool_not_found_behavior="return_error_to_model",
         )
         hooks = ReportUsageHooks(
             model=resolved_model,