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/App.tsx

@@ -401,24 +401,30 @@ function AppContent() {
             )}
           </div>
 
-          {/* ---- 情景选择卡片网格（视频下方） ---- */}
-          <div className="scenario-picker">
-            <div className="scenario-picker__title">
-              <span className="scenario-picker__label">{tr("settings.scenario")}</span>
-              <span className="scenario-picker__active">{activeScenario.icon} {activeScenario.nameKey ? tr(activeScenario.nameKey) : activeScenario.name}</span>
-            </div>
-            <div className="scenario-picker__grid">
+          {/* ---- 情景选择芯片条（视频下方） ---- */}
+          <div className="scenario-strip">
+            <span className="scenario-strip__label">{tr("settings.scenario")}</span>
+            <div className="scenario-strip__scroll">
               {allScenarios.map((sc) => (
                 <button
                   key={sc.id}
-                  className={`scenario-picker__card ${config.scenario === sc.id ? "scenario-picker__card--active" : ""}`}
+                  className={`scenario-chip ${config.scenario === sc.id ? "scenario-chip--active" : ""}`}
                   onClick={() => handleSelectScenario(sc.id)}
                   title={sc.description ? sc.description : sc.descKey ? tr(sc.descKey) : sc.name}
                 >
-                  <span className="scenario-picker__card-icon">{sc.icon}</span>
-                  <span className="scenario-picker__card-name">{sc.nameKey ? tr(sc.nameKey) : sc.name}</span>
+                  <span className="scenario-chip__icon">{sc.icon}</span>
+                  <span className="scenario-chip__name">{sc.nameKey ? tr(sc.nameKey) : sc.name}</span>
                 </button>
               ))}
+              {/* 新建情景快捷入口 */}
+              <button
+                className="scenario-chip scenario-chip--add"
+                onClick={() => setShowCreateScenario(true)}
+                title={tr("scenario.create.button")}
+              >
+                <span className="scenario-chip__icon">+</span>
+                <span className="scenario-chip__name">{tr("scenario.createChip")}</span>
+              </button>
             </div>
           </div>