fix(ui): harden theme toggle accessibility

src/lib/ui/components/ThemeToggle.tsx

@@ -14,7 +14,6 @@ export function ThemeToggle({ theme, onThemeChange }: ThemeToggleProps) {
   return (
     <button
       aria-label={label}
-      aria-pressed={theme === "dark"}
       className="theme-toggle"
       data-ui-theme-toggle="true"
       onClick={() => onThemeChange(nextTheme)}

src/lib/ui/stories/ThemeToggle.stories.tsx

@@ -20,4 +20,9 @@ export const Light: Story = {
   args: {
     theme: "light",
   },
+  parameters: {
+    globals: {
+      theme: "light",
+    },
+  },
 };

src/lib/ui/theme.test.ts

@@ -2,6 +2,7 @@ import { describe, expect, test } from "vitest";
 import {
   getNextUiTheme,
   isUiTheme,
+  persistUiTheme,
   resolveInitialUiTheme,
   UI_THEME_STORAGE_KEY,
 } from "./theme";
@@ -25,6 +26,26 @@ describe("UI theme preference", () => {
     expect(resolveInitialUiTheme(storage)).toBe("dark");
   });
 
+  test("falls back when stored preferences cannot be read", () => {
+    const storage = {
+      getItem() {
+        throw new Error("storage blocked");
+      },
+    };
+
+    expect(resolveInitialUiTheme(storage)).toBe("dark");
+  });
+
+  test("ignores persistence failures", () => {
+    const storage = {
+      setItem() {
+        throw new Error("quota exceeded");
+      },
+    };
+
+    expect(() => persistUiTheme("light", storage)).not.toThrow();
+  });
+
   test("detects and toggles supported themes", () => {
     expect(isUiTheme("light")).toBe(true);
     expect(isUiTheme("dark")).toBe(true);

src/lib/ui/theme.ts

@@ -22,7 +22,7 @@ export function resolveInitialUiTheme(
   storage?: ReadableThemeStorage | null,
   fallback: UiTheme = "dark",
 ): UiTheme {
-  const stored = readStoredTheme(storage);
+  const stored = safeReadStoredTheme(storage);
 
   return isUiTheme(stored) ? stored : fallback;
 }
@@ -33,12 +33,26 @@ export function persistUiTheme(
 ): void {
   if (!storage) return;
 
-  if ("setItem" in storage) {
-    storage.setItem(UI_THEME_STORAGE_KEY, theme);
-    return;
-  }
+  try {
+    if ("setItem" in storage) {
+      storage.setItem(UI_THEME_STORAGE_KEY, theme);
+      return;
+    }
 
-  storage.set(UI_THEME_STORAGE_KEY, theme);
+    storage.set(UI_THEME_STORAGE_KEY, theme);
+  } catch {
+    // Browser storage may be blocked or quota-constrained.
+  }
+}
+
+function safeReadStoredTheme(
+  storage?: ReadableThemeStorage | null,
+): string | undefined {
+  try {
+    return readStoredTheme(storage);
+  } catch {
+    return undefined;
+  }
 }
 
 function readStoredTheme(