feat(openai): 增加 gpt-5.4-mini/nano 模型支持与定价配置

- 接入 gpt-5.4-mini/nano 模型识别与规范化，补充默认模型列表
- 增加 gpt-5.4-mini/nano 输入/缓存命中/输出价格与计费兜底逻辑
- 同步前端模型白名单与 OpenCode 配置
- 补充 service tier(priority/flex) 计费回归测试

frontend/src/components/keys/UseKeyModal.vue

@@ -705,6 +705,38 @@ function generateOpenCodeConfig(platform: string, baseUrl: string, apiKey: strin
         xhigh: {}
       }
     },
+    'gpt-5.4-mini': {
+      name: 'GPT-5.4 Mini',
+      limit: {
+        context: 400000,
+        output: 128000
+      },
+      options: {
+        store: false
+      },
+      variants: {
+        low: {},
+        medium: {},
+        high: {},
+        xhigh: {}
+      }
+    },
+    'gpt-5.4-nano': {
+      name: 'GPT-5.4 Nano',
+      limit: {
+        context: 400000,
+        output: 128000
+      },
+      options: {
+        store: false
+      },
+      variants: {
+        low: {},
+        medium: {},
+        high: {},
+        xhigh: {}
+      }
+    },
     'gpt-5.3-codex-spark': {
       name: 'GPT-5.3 Codex Spark',
       limit: {