feat: Add support for local Ollama provider

This commit introduces support for using a local Ollama instance as an alternative AI provider. Key changes: - Added the `ollama` npm package. - Added a provider selection UI to the main page, allowing users to choose between "Together AI" and "Ollama". - Updated the `createChat` server action to conditionally use the `ollama` library for chat creation, title generation, and screenshot analysis. - Updated the streaming API endpoint to support streaming responses from Ollama. - Used dynamic imports for the `ollama` library to prevent it from being bundled on the client.