feat(openai): 增加 gpt-5.4 模型支持与定价配置

- 接入 gpt-5.4 模型识别与规范化，补充默认模型列表
- 增加 gpt-5.4 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 上下文窗口（1050000/128000）

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
(cherry picked from commit 924476dcac6181cd0f3ee731ec7b73672ff03793)

backend/resources/model-pricing/model_prices_and_context_window.json

@@ -5140,6 +5140,39 @@
     "supports_vision": true,
     "supports_web_search": true
   },
+  "gpt-5.4": {
+    "cache_read_input_token_cost": 2.5e-07,
+    "input_cost_per_token": 2.5e-06,
+    "litellm_provider": "openai",
+    "max_input_tokens": 1050000,
+    "max_output_tokens": 128000,
+    "max_tokens": 128000,
+    "mode": "chat",
+    "output_cost_per_token": 1.5e-05,
+    "supported_endpoints": [
+      "/v1/chat/completions",
+      "/v1/responses"
+    ],
+    "supported_modalities": [
+      "text",
+      "image"
+    ],
+    "supported_output_modalities": [
+      "text",
+      "image"
+    ],
+    "supports_function_calling": true,
+    "supports_native_streaming": true,
+    "supports_parallel_function_calling": true,
+    "supports_pdf_input": true,
+    "supports_prompt_caching": true,
+    "supports_reasoning": true,
+    "supports_response_schema": true,
+    "supports_service_tier": true,
+    "supports_system_messages": true,
+    "supports_tool_choice": true,
+    "supports_vision": true
+  },
   "gpt-5.3-codex": {
     "cache_read_input_token_cost": 1.75e-07,
     "cache_read_input_token_cost_priority": 3.5e-07,