fix(ollama): include items structure in tool parameter definitions

[wucm667]

Problem

When using Ollama ChatModel with tools that have array-type parameters, the items structure is missing in the tool definition sent to the Ollama API. This causes the model to lack schema information for array elements.

For example, a tool parameter Messages []*message is serialized as:

{
  "messages": {
    "type": "array",
    "description": "Messages to test."
  }
}

Instead of the expected:

{
  "messages": {
    "items": {
      "properties": {
        "title": { "description": "...", "type": "string" },
        "content": { "description": "...", "type": "string" }
      },
      "type": "object"
    },
    "type": "array",
    "description": "Messages to test."
  }
}

Fix

Add a recursive schemaToToolProperty helper that converts *jsonschema.Schema to api.ToolProperty, properly handling:

• Type / TypeEnhanced
• Items (recursive for array element types)
• AnyOf (recursive for union types)
• Description, Enum

Replaces the previous flat property construction that only handled top-level Type, Description, and Enum.

Closes #716