feat(providers): add Ollama local provider (`internal/providers/ollama`)

[Nithwin]

Is your feature request related to a problem? Please describe.

Goal

Enable developers to run WindMist with zero API rate limits and zero cost by connecting to local models via Ollama.

Describe the solution you'd like

Requirements

1. Create internal/providers/ollama/provider.go implementing ai.Provider (Generate, Stream).
2. Connect to the local server endpoint (http://localhost:11434/v1).
3. Support native tool calling schemas for open-source models like llama3.1 and qwen2.5.
4. Register dynamically via ai.Register("ollama", New) inside init().

Describe alternatives you've considered

No response

Additional Context

No response