fix: use eu-central-1 Bedrock model ID (eu.anthropic.claude-sonnet-4-6) (#4)

The us. prefix doesn't work in eu-central-1 region.

Co-authored-by: overthelex <mcvovkes@gmail.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

src/lmaf/core/config.py

@@ -15,7 +15,7 @@ class Config:
 
     # LLM provider
     default_provider: str = "anthropic"
-    default_model: str = "us.anthropic.claude-sonnet-4-6-20250514-v1:0"
+    default_model: str = "eu.anthropic.claude-sonnet-4-6"
 
     # Per-agent model overrides
     model_overrides: dict[str, str] = field(default_factory=dict)