fix: locale toggle shows current language, date inputs respect locale

- Language switcher now displays current locale (中文/English) instead of target
- Add lang attribute to date inputs for proper localization of native date picker

components/Sidebar.tsx

@@ -101,7 +101,7 @@ export function Sidebar() {
           style={{ color: "var(--text-muted)", background: "var(--row-hover)", border: "1px solid var(--surface-border)" }}
         >
           <Languages className="h-3.5 w-3.5" />
-          <span className="font-medium">{locale === "zh" ? "English" : "中文"}</span>
+          <span className="font-medium">{locale === "zh" ? "中文" : "English"}</span>
         </button>
 
         {/* Status */}