fix: correct Qwen3.8 Max China pricing (#4049)

providers/alibaba-cn/models/qwen3.8-max.toml

@@ -2,9 +2,9 @@
 # https://www.qianwenai.com/models/qwen3.8-max
 # https://help.aliyun.com/zh/model-studio/model-pricing (Beijing: qwen3.8-max ¥12/¥36)
 # https://platform.qianwenai.com/docs/developer-guides/text-generation/thinking
+# CNY→USD rate: 6.7513, 2026-08-02, source: https://www.nimbuscalc.com/calculators/financial-calculators/currency-converter/USD-CNY-2026-08-02/
 # CNY list: input ¥12, output ¥36, implicit cache hit ¥1.5, explicit cache create ¥15,
-# explicit cache read ¥1 (per 1M tokens). USD via Alibaba EN Beijing parity for the
-# same CNY list as qwen3.7-max ($1.65/$4.951 for ¥12/¥36); cache scaled from CNY ratios.
+# explicit cache read ¥1 (per 1M tokens).
 # Toggle: enable_thinking true|false (hybrid)
 # Effort: reasoning_effort = low|medium|xhigh (default xhigh); high accepted as alias → xhigh
 # Budget: thinking_budget (0..262144) cannot be combined with reasoning_effort
@@ -21,7 +21,7 @@ reasoning_options = [
 field = "reasoning_content"
 
 [cost]
-input = 1.65
-output = 4.951
-cache_read = 0.206
-cache_write = 2.0625
+input = 1.77744
+output = 5.33231
+cache_read = 0.22218
+cache_write = 2.22179