feat: persist theme prefs in localStorage for reliable same-device persistence

- Add src/lib/local-theme-prefs.ts: read/write color theme, radius, sidebar
  config to localStorage key 'isletmem-theme-prefs'
- ThemeCustomizer: init state from localStorage (falls back to Appwrite prefs),
  save to localStorage on every color/radius/sidebar change in addition to Appwrite
- PrefsInitializer: merge localStorage (wins) with server Appwrite prefs on mount

Appwrite updatePrefs had a silent try/catch so failures were invisible;
dark/light was already in localStorage via ThemeProvider but color theme was not.

src/components/theme-customizer/prefs-initializer.tsx

@@ -7,6 +7,7 @@ import { useTheme } from "@/hooks/use-theme";
 import { useThemeManager } from "@/hooks/use-theme-manager";
 import { tweakcnThemes } from "@/config/theme-data";
 import type { ThemePrefs } from "@/lib/appwrite/theme-prefs-actions";
+import { getLocalThemePrefs } from "@/lib/local-theme-prefs";
 
 export function PrefsInitializer({ prefs }: { prefs: ThemePrefs }) {
   const { setTheme } = useTheme();
@@ -18,30 +19,40 @@ export function PrefsInitializer({ prefs }: { prefs: ThemePrefs }) {
     if (applied.current) return;
     applied.current = true;
 
-    if (prefs.theme) setTheme(prefs.theme);
+    // localStorage wins (most recent change on this device); Appwrite prefs are fallback
+    const local = getLocalThemePrefs();
+    const effectiveTheme = prefs.theme;
+    const effectiveColorTheme = local.colorTheme ?? prefs.colorTheme;
+    const effectiveTweakcnTheme = local.tweakcnTheme ?? prefs.tweakcnTheme;
+    const effectiveRadius = local.radius ?? prefs.radius;
+    const effectiveSidebarVariant = (local.sidebarVariant as ThemePrefs["sidebarVariant"]) ?? prefs.sidebarVariant;
+    const effectiveSidebarCollapsible = (local.sidebarCollapsible as ThemePrefs["sidebarCollapsible"]) ?? prefs.sidebarCollapsible;
+    const effectiveSidebarSide = (local.sidebarSide as ThemePrefs["sidebarSide"]) ?? prefs.sidebarSide;
+
+    if (effectiveTheme) setTheme(effectiveTheme);
 
     const isDark =
-      prefs.theme === "dark" ||
-      (prefs.theme !== "light" &&
+      effectiveTheme === "dark" ||
+      (effectiveTheme !== "light" &&
         typeof window !== "undefined" &&
         window.matchMedia("(prefers-color-scheme: dark)").matches);
 
-    if (prefs.radius) applyRadius(prefs.radius);
+    if (effectiveRadius) applyRadius(effectiveRadius);
 
-    if (prefs.colorTheme) {
-      applyTheme(prefs.colorTheme, isDark);
+    if (effectiveColorTheme) {
+      applyTheme(effectiveColorTheme, isDark);
     }
 
-    if (prefs.tweakcnTheme) {
-      const preset = tweakcnThemes.find((t) => t.value === prefs.tweakcnTheme)?.preset;
+    if (effectiveTweakcnTheme) {
+      const preset = tweakcnThemes.find((t) => t.value === effectiveTweakcnTheme)?.preset;
       if (preset) applyTweakcnTheme(preset, isDark);
     }
 
-    if (prefs.sidebarVariant || prefs.sidebarCollapsible || prefs.sidebarSide) {
+    if (effectiveSidebarVariant || effectiveSidebarCollapsible || effectiveSidebarSide) {
       updateConfig({
-        ...(prefs.sidebarVariant && { variant: prefs.sidebarVariant }),
-        ...(prefs.sidebarCollapsible && { collapsible: prefs.sidebarCollapsible }),
-        ...(prefs.sidebarSide && { side: prefs.sidebarSide }),
+        ...(effectiveSidebarVariant && { variant: effectiveSidebarVariant }),
+        ...(effectiveSidebarCollapsible && { collapsible: effectiveSidebarCollapsible }),
+        ...(effectiveSidebarSide && { side: effectiveSidebarSide }),
       });
     }
     // eslint-disable-next-line react-hooks/exhaustive-deps