🐛 fix(ui): ensure consistent background colors for header action buttons

Fix background color rendering issues for notification bell, theme toggle,
and language switcher buttons in the header bar. These buttons were missing
!important declarations in their CSS classes, causing inconsistent styling
across different devices where other styles could override the intended
background colors.

Changes:
- Add !important to background color classes for notification button
- Add !important to background color classes for theme toggle button
- Add !important to background color classes for language switcher button
- Ensure all header action buttons now have consistent styling matching
  the user avatar dropdown button

This resolves visual inconsistencies where these buttons would appear
without proper background colors on certain devices or screen configurations.

web/src/components/layout/HeaderBar.js

@@ -468,7 +468,7 @@ const HeaderBar = () => {
               onClick={() => setNoticeVisible(true)}
               theme="borderless"
               type="tertiary"
-              className="!p-1.5 !text-current focus:!bg-semi-color-fill-1 dark:focus:!bg-gray-700 !rounded-full bg-semi-color-fill-0 dark:bg-semi-color-fill-1 hover:bg-semi-color-fill-1 dark:hover:bg-semi-color-fill-2"
+              className="!p-1.5 !text-current focus:!bg-semi-color-fill-1 dark:focus:!bg-gray-700 !rounded-full !bg-semi-color-fill-0 dark:!bg-semi-color-fill-1 hover:!bg-semi-color-fill-1 dark:hover:!bg-semi-color-fill-2"
             />
 
             <Button
@@ -477,7 +477,7 @@ const HeaderBar = () => {
               onClick={() => setTheme(theme === 'dark' ? false : true)}
               theme="borderless"
               type="tertiary"
-              className="!p-1.5 !text-current focus:!bg-semi-color-fill-1 dark:focus:!bg-gray-700 !rounded-full bg-semi-color-fill-0 dark:bg-semi-color-fill-1 hover:bg-semi-color-fill-1 dark:hover:bg-semi-color-fill-2"
+              className="!p-1.5 !text-current focus:!bg-semi-color-fill-1 dark:focus:!bg-gray-700 !rounded-full !bg-semi-color-fill-0 dark:!bg-semi-color-fill-1 hover:!bg-semi-color-fill-1 dark:hover:!bg-semi-color-fill-2"
             />
 
             <Dropdown
@@ -506,7 +506,7 @@ const HeaderBar = () => {
                 aria-label={t('切换语言')}
                 theme="borderless"
                 type="tertiary"
-                className="!p-1.5 !text-current focus:!bg-semi-color-fill-1 dark:focus:!bg-gray-700 !rounded-full bg-semi-color-fill-0 dark:bg-semi-color-fill-1 hover:bg-semi-color-fill-1 dark:hover:bg-semi-color-fill-2"
+                className="!p-1.5 !text-current focus:!bg-semi-color-fill-1 dark:focus:!bg-gray-700 !rounded-full !bg-semi-color-fill-0 dark:!bg-semi-color-fill-1 hover:!bg-semi-color-fill-1 dark:hover:!bg-semi-color-fill-2"
               />
             </Dropdown>