refactor: 情景选择从卡片网格改为横向滚动芯片条

- 将 scenario-picker 网格布局改为 scenario-strip 横向滚动芯片条
- 新增「新建情景」快捷入口芯片（+按钮）
- 新增 scenario.createChip 三语言翻译键

frontend/src/lib/i18n/en-US.ts

@@ -174,6 +174,7 @@ export const enUS: TranslationMap = {
   "settings.scenario.custom": "My Scenarios",
   "settings.scenario.empty": "No custom scenarios yet. Click the button above to create one.",
   "scenario.create.button": "New Scenario",
+  "scenario.createChip": "New",
   "scenario.create.title": "Create Custom Scenario",
   "scenario.edit.title": "Edit Scenario",
   "scenario.create.name": "Scenario Name",