feat(codex-image): 封装 GPT Image 2 图片接口并收紧错误处理

- 新增 openai:image 路由、planner 与 finalize，内部通过 Codex responses image_generation tool 执行生图

- 补充 Codex OAuth/header 兼容、图片 success report 本地处理与相关前后端/集成测试

- 禁止 chat/completions 使用 gpt-image-2，图片接口限制 n=1，并移除 Provider 模型页的图片能力开关

apps/aether-gateway/src/api/ai/openai.rs

@@ -3,6 +3,7 @@ pub(crate) fn normalized_signature(api_format: &str) -> Option<&'static str> {
         "openai:chat" => Some("openai:chat"),
         "openai:cli" => Some("openai:cli"),
         "openai:compact" => Some("openai:compact"),
+        "openai:image" => Some("openai:image"),
         "openai:video" => Some("openai:video"),
         _ => None,
     }
@@ -13,6 +14,7 @@ pub(crate) fn local_path(api_format: &str) -> Option<&'static str> {
         "openai" | "openai:chat" => Some("/v1/chat/completions"),
         "openai:cli" => Some("/v1/responses"),
         "openai:compact" => Some("/v1/responses/compact"),
+        "openai:image" => Some("/v1/images/generations"),
         "openai:video" => Some("/v1/videos"),
         _ => None,
     }

apps/aether-gateway/src/api/ai/registry.rs

@@ -13,6 +13,8 @@ const AI_POST_ROUTE_PATTERNS: &[&str] = &[
     "/v1/messages/count_tokens",
     "/v1/responses",
     "/v1/responses/compact",
+    "/v1/images/generations",
+    "/v1/images/edits",
 ];
 
 const AI_ANY_ROUTE_PATTERNS: &[&str] = &[