[FEATURE]: Add thinking/reasoning support for GLM-4.7, Kimi K2.5, and MiniMax M2.1 on Zen #12396

#### Steps to reproduce

  Tested via `opencode.json` model config with three configurations across all four Zen
  models.

  **Config A — Thinking + interleaved:**
  ```json
  {
    "provider": {
      "opencode": {
        "models": {
          "<model>": {
            "options": {
              "thinking": { "type": "enabled", "budgetTokens": 16000 },
              "interleaved": { "field": "reasoning_content" }
            }
          }
        }
      }
    }
  }

  Config B — Thinking only (no interleaved):
  "options": {
    "thinking": { "type": "enabled", "budgetTokens": 16000 }
  }

  Config C — No config (empty model entry):
  "<model>": {}

  Test command:
  timeout 60 opencode run "What is 2+2? Think step by step." -m opencode/<model> --format
  json

  Results:
  ┌───────────────────┬──────────────────────────┬────────────────────┬──────────────────┐
  │       Model       │  Config A (thinking +    │ Config B (thinking │  Config C (no    │
  │                   │       interleaved)       │        only)       │     config)      │
  ├───────────────────┼──────────────────────────┼────────────────────┼──────────────────┤
  │ kimi-k2.5-free    │ Works (reasoning > 0)    │ Works (reasoning > │ Works            │
  │                   │                          │  0)                │ (reasoning: 0)   │
  ├───────────────────┼──────────────────────────┼────────────────────┼──────────────────┤
  │ kimi-k2.5 (paid)  │ Rejected                 │ Rejected           │ Works            │
  │                   │                          │                    │ (reasoning: 0)   │
  ├───────────────────┼──────────────────────────┼────────────────────┼──────────────────┤
  │ glm-4.7 (paid)    │ Rejected                 │ Rejected           │ Works            │
  │                   │                          │                    │ (reasoning: 0)   │
  ├───────────────────┼──────────────────────────┼────────────────────┼──────────────────┤
  │ minimax-m2.1      │ Rejected                 │ Rejected           │ Works            │
  │ (paid)            │                          │                    │ (reasoning: 0)   │
  └───────────────────┴──────────────────────────┴────────────────────┴──────────────────┘
  Error messages:
  - glm-4.7: Extra inputs are not permitted, field: 'thinking' — Zen doesn't recognize the
   field at all
  - kimi-k2.5 (paid) and minimax-m2.1: Input should be 'disabled', field:
  'thinking.ThinkingConfigDisabled.type' — field exists but only accepts disabled

  Only kimi-k2.5-free accepts thinking config (both A and B) and returns reasoning tokens.
   All three paid models reject it.