Fix Claude model name format

Use correct model ID with dashes instead of dots:
claude-sonnet-4-5-20250929 (not claude-sonnet-4.5-20250929)

Fixes: 404 "model not found" error in agent execution

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <[email protected]>

Author: amrit110

src/aieng_bot/config.py

@@ -12,7 +12,7 @@ def get_model_name() -> str:
     Returns
     -------
     str
-        The full model identifier (e.g., "claude-sonnet-4.5-20250929").
+        The full model identifier (e.g., "claude-sonnet-4-5-20250929").
 
     """
-    return os.getenv("CLAUDE_MODEL", "claude-sonnet-4.5-20250929")
+    return os.getenv("CLAUDE_MODEL", "claude-sonnet-4-5-20250929")