refactor: deduplicate and improve OpenAI Responses API conversion

- Extract shared map_responses_stop_reason and build_anthropic_usage_from_responses into transform_responses.rs as pub(crate)
- Align cache token extraction priority: OpenAI nested details as fallback, direct Anthropic fields as override
- Extract resolve_content_index helper to eliminate 3x copy-paste in streaming_responses.rs
- Add streaming reasoning/thinking event handlers (response.reasoning.delta/done)
- Add explanatory comment to transform_response heuristic detection
- Add openai_responses to api_format doc comment and needs_transform test
- Add explicit no-op match arms for lifecycle events
- Add promptCacheKey to TS ProviderMeta type
- Update toast i18n key to be generic for both OpenAI formats (zh/en/ja)

src/i18n/locales/en.json

@@ -170,6 +170,7 @@
     "settingsSaved": "Settings saved",
     "settingsSaveFailed": "Failed to save settings: {{error}}",
     "openAIChatFormatHint": "This provider uses OpenAI Chat format and requires the proxy service to be enabled",
+    "openAIFormatHint": "This provider uses OpenAI-compatible format and requires the proxy service to be enabled",
     "openLinkFailed": "Failed to open link",
     "openclawModelsRegistered": "Models have been registered to /model list",
     "openclawDefaultModelSet": "Set as default model",

src/i18n/locales/ja.json

@@ -170,6 +170,7 @@
     "settingsSaved": "設定を保存しました",
     "settingsSaveFailed": "設定の保存に失敗しました: {{error}}",
     "openAIChatFormatHint": "このプロバイダーは OpenAI Chat フォーマットを使用しており、プロキシサービスの有効化が必要です",
+    "openAIFormatHint": "このプロバイダーは OpenAI 互換フォーマットを使用しており、プロキシサービスの有効化が必要です",
     "openLinkFailed": "リンクを開けませんでした",
     "openclawModelsRegistered": "モデルが /model リストに登録されました",
     "openclawDefaultModelSet": "デフォルトモデルに設定しました",

src/i18n/locales/zh.json

@@ -170,6 +170,7 @@
     "settingsSaved": "设置已保存",
     "settingsSaveFailed": "保存设置失败：{{error}}",
     "openAIChatFormatHint": "此供应商使用 OpenAI Chat 格式，需要开启代理服务才能正常使用",
+    "openAIFormatHint": "此供应商使用 OpenAI 兼容格式，需要开启代理服务才能正常使用",
     "openLinkFailed": "链接打开失败",
     "openclawModelsRegistered": "模型已注册到 /model 列表",
     "openclawDefaultModelSet": "已设为默认模型",