feat: add Claude backend with automatic Ollama fallback (Claudification Phase 1)

All agents now prefer Claude API when ANTHROPIC_API_KEY is configured,
with automatic fallback to Ollama when offline or unconfigured. New
src/anthropic/ module provides model selection via get_model() factory.

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

src/agents/librarian/agent.py

@@ -143,16 +143,10 @@ _librarian_agent: Optional[Agent[None, str]] = None
 
 def _create_librarian_agent() -> Agent[None, str]:
     """Create the Librarian PydanticAI agent."""
-    from pydantic_ai.models.openai import OpenAIChatModel
+    from src.anthropic.model_selector import get_model
 
-    from src.ollama.provider import get_ollama_provider
-
-    # Create Ollama model with sanitized provider
-    # (fixes 'content: null' issue with tool calls)
-    model = OpenAIChatModel(
-        model_name=config.OLLAMA_DEFAULT_MODEL,
-        provider=get_ollama_provider(),
-    )
+    # Get best available model (Claude if available, else Ollama)
+    model = get_model()
 
     agent: Agent[None, str] = Agent(
         model=model,
@@ -182,9 +176,12 @@ def _create_librarian_agent() -> Agent[None, str]:
     agent.tool_plain(update_wiki_page)
     agent.tool_plain(smart_create_wiki_page)
 
+    from src.anthropic.model_selector import get_model_info
+    model_info = get_model_info()
     logger.info(
         "librarian_agent_created",
-        model=config.OLLAMA_DEFAULT_MODEL,
+        backend=model_info["backend"],
+        model=model_info["model"],
         tool_count=14,  # 7 research + 3 web + 1 wiki read + 3 wiki write
     )