feat(ai): add support for Ollama AI provider configuration

* Update README with Ollama integration details
* Add Ollama configuration to example YAML files
* Implement Ollama provider in AI factory
* Add tests for Ollama provider functionality
* Enhance config validation for Ollama settings

configs/config.example.yaml

@@ -45,6 +45,10 @@ ai:
     request_headers: {}
     embedding_model: "openrouter/openai/text-embedding-3-small"
     metadata_model: "gpt-4o-mini"
+  ollama:
+    base_url: "http://localhost:11434/v1"
+    api_key: "ollama"
+    request_headers: {}
   openrouter:
     base_url: "https://openrouter.ai/api/v1"
     api_key: ""