refactor(antigravity): haiku 模型映射到 sonnet

backend/internal/service/antigravity_gateway_service.go

@@ -49,11 +49,11 @@ var antigravityPrefixMapping = []struct {
 	{"gemini-3-pro-image", "gemini-3-pro-image"}, // gemini-3-pro-image-preview 等
 	{"claude-3-5-sonnet", "claude-sonnet-4-5"},   // 旧版 claude-3-5-sonnet-xxx
 	{"claude-sonnet-4-5", "claude-sonnet-4-5"},   // claude-sonnet-4-5-xxx
-	{"claude-haiku-4-5", "gemini-3-flash"},       // claude-haiku-4-5-xxx
+	{"claude-haiku-4-5", "claude-sonnet-4-5"},    // claude-haiku-4-5-xxx → sonnet
 	{"claude-opus-4-5", "claude-opus-4-5-thinking"},
-	{"claude-3-haiku", "gemini-3-flash"}, // 旧版 claude-3-haiku-xxx
+	{"claude-3-haiku", "claude-sonnet-4-5"}, // 旧版 claude-3-haiku-xxx → sonnet
 	{"claude-sonnet-4", "claude-sonnet-4-5"},
-	{"claude-haiku-4", "gemini-3-flash"},
+	{"claude-haiku-4", "claude-sonnet-4-5"}, // → sonnet
 	{"claude-opus-4", "claude-opus-4-5-thinking"},
 	{"gemini-3-pro", "gemini-3-pro-high"}, // gemini-3-pro, gemini-3-pro-preview 等
 }