feat: add OpenAI-compatible and Ollama model providers

[philipph-askui]

• Add OpenAIVlmProvider and OpenAIImageQAProvider as generic providers for any OpenAI-compatible API (OpenAI, vLLM, LM Studio, Together AI, etc.)
  • Add OllamaVlmProvider and OllamaImageQAProvider as thin convenience wrappers with Ollama defaults (base_url=http://localhost:11434/v1, dummy API key)
  • Add default pricing entries for GPT-5.4 models

Example:

  from askui import AgentSettings, ComputerAgent
  from askui.model_providers import OllamaVlmProvider

  agent = ComputerAgent(settings=AgentSettings(
      vlm_provider=OllamaVlmProvider(model_id="qwen3.5"),
  ))