Major UI refresh: sidebar redesign, theme expansion, and chat performance optimizations (#706)

## Summary
Complete sidebar redesign and comprehensive UI polish pass with performance optimizations, theme system refinements, and desktop integration improvements.

## Key Changes

**Sidebar & Navigation Redesign**
- Redesigned sessions sidebar layout with unified button primitives
- Added activity sections with project grouping and improved session organization
- Refined sidebar corners, spacing, and visual hierarchy
- Removed NavRail component in favor of streamlined sidebar
- Stabilized sessions bar toggle position in fullscreen mode

**Performance Optimizations**
- Reduced chat streaming CPU usage and storage churn
- Optimized task tool polling and live timers with debouncing
- Prevented chat state races and reduced background request load
- Debounced draft writes and coalesced session reloads
- Optimized message store updates and turn tracking

**Theme & Visual System**
- Added theme-aware window corners (desktop) and border radius tokens
- Introduced glassmorphism effects on desktop sidebar
- Added backdrop blur to UI elements

**Chat Experience**
- Added session-based permission auto-accept toggle in chat input
- Polished permission shield UX with improved icon sizing and spacing
- Fixed chat scroll-to-bottom behavior and timeline tracking
- Enhanced tool output display with better path label detection
- Removed duplicate draft context details in chat header
- Added text selection menu to chat messages

**Git Improvements**
- Refreshed git history visual design with cleaner dividers
- Added remote removal action in sync selector
- Stabilized git polling to prevent excessive requests
- Improved tool output rendering for git operations

**Settings & Panels**
- Fixed mobile scrolling on settings pages
- Made outside-click settings close instantly
- Reduced settings load churn and CPU spikes
- Improved services dropdown layout and spacing
- Softened panel resize handles

**Desktop Integration**
- Synced macOS window theme with app theme
- Restored window dragging in sidebar header zones
- Fixed system window corners on macOS
- Improved header session metadata and action controls

**Button & Component Standardization**
- Unified button primitives across all components
- Standardized destructive action patterns
- Removed unused button variants (button-large, button-small)
- Aligned context tab close hit areas

---------

Co-authored-by: Iuliia Ivashko <yulia.ivashko@gmail.com>

packages/ui/src/components/sections/commands/CommandsSidebar.tsx

@@ -1,6 +1,5 @@
 import React from 'react';
-import { ButtonSmall } from '@/components/ui/button-small';
-import { ButtonLarge } from '@/components/ui/button-large';
+import { Button } from '@/components/ui/button';
 import { Input } from '@/components/ui/input';
 import { toast } from '@/components/ui';
 import { isMobileDeviceViaCSS } from '@/lib/device';
@@ -221,13 +220,13 @@ export const CommandsSidebar: React.FC<CommandsSidebarProps> = ({ onItemSelect }
         <SettingsProjectSelector className="mb-3" />
         <div className="flex items-center justify-between gap-2">
           <span className="typography-meta text-muted-foreground">Total {commandOnlyItems.length}</span>
-          <ButtonSmall
+          <Button size="sm"
             variant="ghost"
             className="h-7 w-7 px-0 -my-1 text-muted-foreground"
             onClick={handleCreateNew}
           >
             <RiAddLine className="h-3.5 w-3.5" />
-          </ButtonSmall>
+          </Button>
         </div>
       </div>
 
@@ -310,16 +309,17 @@ export const CommandsSidebar: React.FC<CommandsSidebarProps> = ({ onItemSelect }
             </DialogDescription>
           </DialogHeader>
           <DialogFooter>
-            <ButtonLarge
+            <Button
+              size="sm"
               variant="ghost"
               onClick={closeConfirmActionDialog}
               disabled={isConfirmActionPending}
             >
               Cancel
-            </ButtonLarge>
-            <ButtonLarge onClick={handleConfirmAction} disabled={isConfirmActionPending}>
+            </Button>
+            <Button size="sm" onClick={handleConfirmAction} disabled={isConfirmActionPending}>
               {confirmActionType === 'delete' ? 'Delete' : 'Reset'}
-            </ButtonLarge>
+            </Button>
           </DialogFooter>
         </DialogContent>
       </Dialog>
@@ -345,15 +345,16 @@ export const CommandsSidebar: React.FC<CommandsSidebarProps> = ({ onItemSelect }
             }}
           />
           <DialogFooter>
-            <ButtonLarge
+            <Button
+              size="sm"
               variant="ghost"
               onClick={() => setRenameDialogCommand(null)}
             >
               Cancel
-            </ButtonLarge>
-            <ButtonLarge onClick={handleRenameCommand}>
+            </Button>
+            <Button size="sm" onClick={handleRenameCommand}>
               Rename
-            </ButtonLarge>
+            </Button>
           </DialogFooter>
         </DialogContent>
       </Dialog>
@@ -422,12 +423,12 @@ const CommandListItem: React.FC<CommandListItemProps> = ({
 
         <DropdownMenu open={isMenuOpen} onOpenChange={onMenuOpenChange}>
           <DropdownMenuTrigger asChild>
-            <ButtonSmall
+            <Button size="sm"
               variant="ghost"
               className="h-6 w-6 px-0 flex-shrink-0 -mr-1 opacity-100 transition-opacity md:opacity-0 md:group-hover:opacity-100"
             >
               <RiMore2Line className="h-3.5 w-3.5" />
-            </ButtonSmall>
+            </Button>
           </DropdownMenuTrigger>
           <DropdownMenuContent align="end" className="w-fit min-w-20">
             {onRename && (