feat(locale): 实现前端多语言覆盖与生效语言逻辑

- 新增 effectiveLanguage 字段，统一界面语言解析依据
- 支持前端语言覆盖（德语/西班牙语/法语）优先显示，回退设备语言
- setUiLanguage 方法实现前端或设备语言切换逻辑与持久化
- 当设备语言发生变化时自动清除前端语言覆盖，保证同步一致
- BottomNav 组件和 ConnectionPlaceholder 组件调整使用 effectiveLanguage 获取语言包
- 多语言数据更新，新增德语、西班牙语、法语、韩语支持及语言选项扩展

client/src/pages/EQPage.tsx

@@ -110,16 +110,17 @@ export default function EQPage() {
     upgradePeqChange,
     upgradePeqApply,
     syncPeqCatalog,
+    effectiveLanguage,
   } = useDevice();
   const bypassOn = (deviceState?.dsp_enable ?? 0) === 0;
   const peqOn = (deviceState?.peqEnable ?? 0) === 1;
   const eqOn = peqOn && !bypassOn;
 
   const eqUi = useMemo((): PeqEqUi => {
-    const pack = resolveLocalePack(deviceState?.language);
+    const pack = resolveLocalePack(effectiveLanguage);
     const peq = pack.peq as typeof localeZh.peq;
     return (peq.eqUi ?? (localeEn.peq as typeof localeEn.peq).eqUi) as PeqEqUi;
-  }, [deviceState?.language]);
+  }, [effectiveLanguage]);
 
   const firmwareVersion = useMemo(
     () => parseFirmwareVersion(deviceState?.version),
@@ -128,9 +129,9 @@ export default function EQPage() {
   const peqReorderEnabled = supportsPeqPresetRenameAndSort(firmwareVersion);
 
   const peqCardLabels = useMemo(() => {
-    const pack = resolveLocalePack(deviceState?.language);
+    const pack = resolveLocalePack(effectiveLanguage);
     return pack.peq ?? localeEn.peq;
-  }, [deviceState?.language]);
+  }, [effectiveLanguage]);
 
   const eqPageTitle = usePageTitleWithConnection("HP-EQ");