fix: normalize dot-versioned model names for Anthropic API

anthropic/claude-opus-4.6 (OpenRouter format) was being sent as
claude-opus-4.6 to the Anthropic API, which expects claude-opus-4-6
(hyphens, not dots).

normalize_model_name() now converts dots to hyphens after stripping
the provider prefix, matching Anthropic's naming convention.

Fixes 404: 'model: claude-opus-4.6 was not found'

agent/anthropic_adapter.py

@@ -328,10 +328,15 @@ def normalize_model_name(model: str) -> str:
     """Normalize a model name for the Anthropic API.
 
     - Strips 'anthropic/' prefix (OpenRouter format, case-insensitive)
+    - Converts dots to hyphens in version numbers (OpenRouter uses dots,
+      Anthropic uses hyphens: claude-opus-4.6 → claude-opus-4-6)
     """
     lower = model.lower()
     if lower.startswith("anthropic/"):
         model = model[len("anthropic/"):]
+    # OpenRouter uses dots for version separators (claude-opus-4.6),
+    # Anthropic uses hyphens (claude-opus-4-6). Convert dots to hyphens.
+    model = model.replace(".", "-")
     return model