feat(pricing): seed Qwen3.8 Max built-in model pricing (#6053)

* feat(pricing): seed Qwen3.8 Max built-in model pricing

Add insert-if-absent row for qwen3.8-max at 2/6 USD per Mtok input/output with 0.20 cache read.

* fix(pricing): set qwen3.8-max cache write to 2.50

Align cache_write with official explicit context-cache rate (125 percent of input). cache_read stays 0.20 (10 percent hit).

* fix(pricing): correct qwen3.8-max cache read price

---------

Co-authored-by: Jason <farion1231@gmail.com>

src-tauri/src/database/schema.rs

@@ -2237,6 +2237,7 @@ impl Database {
                 "0",
             ),
             // Qwen 系列 (阿里巴巴)
+            ("qwen3.8-max", "Qwen3.8 Max", "2", "6", "0.25", "2.50"),
             ("qwen3.7-max", "Qwen3.7 Max", "2.50", "7.50", "0.25", "0"),
             ("qwen3.7-plus", "Qwen3.7 Plus", "0.40", "1.60", "0.08", "0"),
             (