🪄 refactor: UI Polish and Admin Dialog Unification (#11108)

* refactor(OpenSidebar): removed useless classNames

* style(Header): update hover styles across various components for improved UI consistency

* style(Nav): update hover styles in AccountSettings and SearchBar for improved UI consistency

* style: update button classes for consistent hover effects and improved UI responsiveness

* style(Nav, OpenSidebar, Header, Convo): improve UI responsiveness and animation transitions

* style(PresetsMenu, NewChat): update icon sizes and improve component styling for better UI consistency

* style(Nav, Root): enhance sidebar mobile animations and responsiveness for better UI experience

* style(ExportAndShareMenu, BookmarkMenu): update icon sizes for improved UI consistency

* style: remove transition duration from button classes for improved UI responsiveness

* style(CustomMenu, ModelSelector): update background colors for improved UI consistency and responsiveness

* style(ExportAndShareMenu): update icon color for improved UI consistency

* style(TemporaryChat): refine button styles for improved UI consistency and responsiveness

* style(BookmarkNav): refactor to use DropdownPopup and remove BookmarkNavItems for improved UI consistency and functionality

* style(CustomMenu, EndpointItem): enhance UI elements for improved consistency and accessibility

* style(EndpointItem): adjust gap in icon container for improved layout consistency

* style(CustomMenu, EndpointItem): update focus ring color for improved UI consistency

* style(EndpointItem): update icon color for improved UI consistency in dark theme

* style: update focus styles for improved accessibility and consistency across components

* refactor(Nav): extract sidebar width to NAV_WIDTH constant

Centralize mobile (320px) and desktop (260px) sidebar widths in a single
exported constant to avoid magic numbers and ensure consistency.

* fix(BookmarkNav): memoize handlers used in useMemo

Wrap handleTagClick and handleClear in useCallback and add them to the
dropdownItems useMemo dependency array to prevent stale closures.

* feat: introduce FilterInput component and replace existing inputs with it across multiple components

* feat(DataTable): replace custom input with FilterInput component for improved filtering

* fix: Nested dialog overlay stacking issue

Fixes overlay appearing behind content when opening nested dialogs.
Introduced dynamic z-index calculation based on dialog depth using React context.

- First dialog: overlay z-50, content z-100
- Nested dialogs increment by 60: overlay z-110/content z-160, etc.

Preserves a11y escape key handling from #10975 and #10851.

Regression from #11008 (afb67fcf1) which increased content z-index
without adjusting overlay z-index for nested dialog scenarios.

* Refactor admin settings components to use a unified AdminSettingsDialog

- Removed redundant code from AdminSettings, MCPAdminSettings, and Memories AdminSettings components.
- Introduced AdminSettingsDialog component to handle permission management for different sections.
- Updated permission handling logic to use a consistent structure across components.
- Enhanced role selection and permission confirmation features in the new dialog.
- Improved UI consistency and maintainability by centralizing dialog functionality.

* refactor(Memory): memory management UI components and replace MemoryViewer with MemoryPanel

* refactor(Memory): enhance UI components for Memory dialogs and improve input styling

* refactor(Bookmarks): improve bookmark management UI with enhanced styling

* refactor(translations): remove redundant filter input and bookmark count entries

* refactor(Convo): integrate useShiftKey hook for enhanced keyboard interaction and improve UI responsiveness

client/src/hooks/Generic/index.ts

@@ -1 +1,2 @@
 export * from './useLazyEffect';
+export { default as useShiftKey } from './useShiftKey';

client/src/hooks/Generic/useShiftKey.ts

@@ -0,0 +1,47 @@
+import { useState, useEffect } from 'react';
+
+/**
+ * Hook to track whether the shift key is currently being held down.
+ * Ignores shift when Alt is also pressed to avoid conflicts with
+ * accessibility keyboard shortcuts (Shift+Alt is used for screen readers).
+ * @returns boolean indicating if shift key is pressed (without Alt)
+ */
+export default function useShiftKey(): boolean {
+  const [isShiftHeld, setIsShiftHeld] = useState(false);
+
+  useEffect(() => {
+    const handleKeyDown = (e: KeyboardEvent) => {
+      // Only set shift if Alt is not pressed (Alt+Shift is used for a11y)
+      if (e.key === 'Shift' && !e.altKey) {
+        setIsShiftHeld(true);
+      }
+      // If Alt is pressed while shift is held, reset shift state
+      if (e.key === 'Alt' && e.shiftKey) {
+        setIsShiftHeld(false);
+      }
+    };
+
+    const handleKeyUp = (e: KeyboardEvent) => {
+      if (e.key === 'Shift') {
+        setIsShiftHeld(false);
+      }
+    };
+
+    // Reset shift state when window loses focus
+    const handleBlur = () => {
+      setIsShiftHeld(false);
+    };
+
+    window.addEventListener('keydown', handleKeyDown);
+    window.addEventListener('keyup', handleKeyUp);
+    window.addEventListener('blur', handleBlur);
+
+    return () => {
+      window.removeEventListener('keydown', handleKeyDown);
+      window.removeEventListener('keyup', handleKeyUp);
+      window.removeEventListener('blur', handleBlur);
+    };
+  }, []);
+
+  return isShiftHeld;
+}