refactor: consolidate Ollama model configuration

- Add OLLAMA_EMBEDDING_MODEL for embeddings (nomic-embed-text)
- OLLAMA_MODEL now used for all LLM operations (mistral-nemo-large:latest)
- Remove separate reranker_model setting
- Update WikiPageWriter to use settings instead of hardcoded model
- Improves VRAM efficiency by keeping one model hot

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

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

src/core/dependencies.py

@@ -113,7 +113,7 @@ def get_ollama_client() -> OllamaClient:
     settings = get_settings()
     client = OllamaClient(
         base_url=settings.ollama_url,
-        model=settings.ollama_model
+        model=settings.ollama_embedding_model
     )
     logger.debug("Created Ollama client instance")
     return client