fix: unify theme system - fix theme switching persistence

- Unified localStorage key to 'theme-preference' across all components
- Fixed header.tsx using wrong localStorage key ('theme' instead of 'theme-preference')
- Added localStorage hybrid persistence for instant theme changes
- Removed router.refresh() which was causing stale data revert
- Replaced Blue theme with Sepia
- Consolidated auth() calls to prevent race conditions
- Updated UserSettingsData types to include all themes

keep-notes/lib/i18n/load-translations.ts

@@ -25,6 +25,14 @@ export interface Translations {
     rememberMe: string
     orContinueWith: string
   }
+  sidebar: {
+    notes: string
+    reminders: string
+    labels: string
+    editLabels: string
+    archive: string
+    trash: string
+  }
   notes: {
     title: string
     newNote: string

keep-notes/lib/theme-script.ts

@@ -0,0 +1,31 @@
+export function getThemeScript(theme: string = 'light') {
+  return `
+    (function() {
+      try {
+        var localTheme = localStorage.getItem('theme-preference');
+        var theme = localTheme || '${theme}';
+        var root = document.documentElement;
+        
+        root.classList.remove('dark');
+        root.removeAttribute('data-theme');
+
+        if (theme === 'auto') {
+          if (window.matchMedia('(prefers-color-scheme: dark)').matches) {
+            root.classList.add('dark');
+          }
+        } else if (theme === 'dark') {
+          root.classList.add('dark');
+        } else if (theme === 'light') {
+          // do nothing
+        } else {
+          root.setAttribute('data-theme', theme);
+          if (theme === 'midnight') {
+            root.classList.add('dark');
+          }
+        }
+      } catch (e) {
+        console.error('Theme script error', e);
+      }
+    })();
+  `
+}