[FEATURE]: Add disable_reasoning parameter for GLM/Cerebras thinking toggle #11987

Problem

GLM-4.5/4.6/4.7 and Cerebras models support disable_reasoning boolean parameter to control thinking/reasoning output. Currently no way to configure this in OpenCode agent settings.

• Issue How to disable thinking in GLM-4.6? #3259 asked "How to disable thinking in GLM-4.6?" but closed without implementation
• Useful for reducing tokens, faster responses, avoiding parsing bugs (Error "reasoning part reasoning-0 not found" from tool calls using GLM 4.5 Air #6486, GLM 4.7 thinking process not properly formatted - missing leading tags #7779, GLM 4.7 on Zai coding plan puts tool calls inside the thinking/reasoning tag. #6708)

Proposed Solution

Add disable_reasoning as optional boolean in agent configuration:

{
  "agent": {
    "fast-build": {
      "model": "cerebras/zai-glm-4.7",
      "disable_reasoning": true
    }
  }
}

Benefits

• Reduce token usage/costs for simple tasks
• Faster responses when deep reasoning not needed
• Avoids reasoning tag parsing issues
• User control over thinking verbosity

Implementation Notes

• Apply to GLM and Cerebras providers
• Default: false (thinking enabled)
• Parameter name matches GLM/Cerebras API spec