Merge origin/main into nightly

Resolve conflicts:
- .gitignore: keep nightly additions (.test, skills-lock.json)
- relay/helper/price.go: keep both billingexpr and model imports
- en.json / zh-CN.json: keep nightly's superset of i18n entries
- service/billing_session.go: add missing 3rd arg to DecreaseUserQuota
- en.json / zh-CN.json: deduplicate 129+320 duplicate i18n keys

dto/openai_response.go

@@ -273,7 +273,7 @@ type OpenAIResponsesResponse struct {
 	Status             json.RawMessage    `json:"status"`
 	Error              any                `json:"error,omitempty"`
 	IncompleteDetails  *IncompleteDetails `json:"incomplete_details,omitempty"`
-	Instructions       string             `json:"instructions"`
+	Instructions       json.RawMessage    `json:"instructions"`
 	MaxOutputTokens    int                `json:"max_output_tokens"`
 	Model              string             `json:"model"`
 	Output             []ResponsesOutput  `json:"output"`