fix: remove stale qwen3.7-max references from config.example.toml

v0.8.48 removed the Qwen 3.7 Max preset (it's a hosted model, not open-weight).
Two references remained in config.example.toml:
- Default Models comment (line 41)
- OpenRouter provider section comment (line 280)

These stale references could confuse users into trying a removed model.

config.example.toml

@@ -38,7 +38,6 @@ base_url = "https://api.deepseek.com/beta"
 #   deepseek-ai/deepseek-v4-flash — NVIDIA NIM-hosted Flash model ID
 #   deepseek/deepseek-v4-pro      — default OpenRouter DeepSeek model ID
 #   arcee-ai/trinity-large-thinking — OpenRouter Arcee Trinity Large Thinking
-#   qwen/qwen3.7-max              — OpenRouter Qwen 3.7 Max
 #   xiaomi/mimo-v2.5-pro          — OpenRouter Xiaomi MiMo 2.5 Pro
 #   xiaomi/mimo-v2.5              — OpenRouter Xiaomi MiMo 2.5
 #   gpt-4.1                         — default generic OpenAI-compatible model ID
@@ -278,7 +277,7 @@ max_subagents = 10 # optional (1-20)
 # base_url = "https://openrouter.ai/api/v1"
 # model = "deepseek/deepseek-v4-pro"
 # Recent large model IDs also accepted here include arcee-ai/trinity-large-thinking,
-# qwen/qwen3.7-max, xiaomi/mimo-v2.5-pro, qwen/qwen3.6-35b-a3b,
+# xiaomi/mimo-v2.5-pro, qwen/qwen3.6-35b-a3b,
 # google/gemma-4-31b-it, z-ai/glm-5.1, moonshotai/kimi-k2.6, and
 # nvidia/nemotron-3-nano-omni-30b-a3b-reasoning:free.