fix: remove extra_body tool_choice hack for Claude backend

PydanticAI handles tool_choice natively for Anthropic. The extra_body
hack caused an infinite tool call loop where Claude kept calling the
same tool because tool_choice was forced to "any".

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/anthropic/__init__.py

@@ -7,11 +7,13 @@ Provides model selection with automatic fallback between Claude and Ollama.
 from src.anthropic.model_selector import (
     check_claude_health,
     get_model,
+    get_tool_choice_settings,
     is_claude_available,
 )
 
 __all__ = [
     "check_claude_health",
     "get_model",
+    "get_tool_choice_settings",
     "is_claude_available",
 ]