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/git-identities/GitIdentityEditorDialog.tsx

@@ -1,6 +1,5 @@
 import React from 'react';
 import { Button } from '@/components/ui/button';
-import { ButtonSmall } from '@/components/ui/button-small';
 import { Input } from '@/components/ui/input';
 import { toast } from '@/components/ui';
 import {
@@ -351,7 +350,7 @@ export const GitIdentityEditorDialog: React.FC<GitIdentityEditorDialogProps> = (
                   <div className="flex items-center justify-between gap-4">
                     <span className="typography-ui-label text-foreground">Auth Method</span>
                     <div className="flex items-center gap-1">
-                      <ButtonSmall
+                      <Button size="sm"
                         type="button"
                         variant="outline"
                         onClick={() => setAuthType('ssh')}
@@ -362,8 +361,8 @@ export const GitIdentityEditorDialog: React.FC<GitIdentityEditorDialogProps> = (
                         )}
                       >
                         <RiLock2Line className="w-3.5 h-3.5 mr-1" /> SSH
-                      </ButtonSmall>
-                      <ButtonSmall
+                      </Button>
+                      <Button size="sm"
                         type="button"
                         variant="outline"
                         onClick={() => setAuthType('token')}
@@ -374,7 +373,7 @@ export const GitIdentityEditorDialog: React.FC<GitIdentityEditorDialogProps> = (
                         )}
                       >
                         <RiKeyLine className="w-3.5 h-3.5 mr-1" /> Token
-                      </ButtonSmall>
+                      </Button>
                     </div>
                   </div>
 
@@ -467,7 +466,7 @@ export const GitIdentityEditorDialog: React.FC<GitIdentityEditorDialogProps> = (
             <Button variant="ghost" onClick={() => setIsDeleteDialogOpen(false)} disabled={isDeleting}>
               Cancel
             </Button>
-            <Button size="sm" onClick={() => void handleConfirmDelete()} disabled={isDeleting} className="bg-[var(--status-error)] hover:bg-[var(--status-error)]/90 text-white border-0">
+            <Button size="sm" variant="destructive" onClick={() => void handleConfirmDelete()} disabled={isDeleting}>
               Delete
             </Button>
           </DialogFooter>

packages/ui/src/components/sections/git-identities/GitPage.tsx

@@ -1,5 +1,4 @@
 import React from 'react';
-import { ButtonSmall } from '@/components/ui/button-small';
 import { toast } from '@/components/ui';
 import {
   Dialog,
@@ -10,7 +9,6 @@ import {
   DialogTitle,
 } from '@/components/ui/dialog';
 import { Button } from '@/components/ui/button';
-import { ButtonLarge } from '@/components/ui/button-large';
 import {
   DropdownMenu,
   DropdownMenuContent,
@@ -124,9 +122,9 @@ export const GitPage: React.FC = () => {
               <div className="flex items-center gap-2">
                 <h3 className="typography-ui-header font-semibold text-foreground">Identities</h3>
               </div>
-              <ButtonSmall variant="outline" onClick={() => openEditor('new')}>
+              <Button size="sm" variant="outline" onClick={() => openEditor('new')}>
                 <RiAddLine className="w-3.5 h-3.5 mr-1" /> New
-              </ButtonSmall>
+              </Button>
             </div>
 
             <div className="rounded-lg bg-[var(--surface-elevated)]/70 overflow-hidden flex flex-col">
@@ -213,9 +211,9 @@ export const GitPage: React.FC = () => {
             <Button variant="ghost" onClick={() => setDeleteDialogProfile(null)} disabled={isDeletePending}>
               Cancel
             </Button>
-            <ButtonLarge onClick={() => void handleConfirmDelete()} disabled={isDeletePending} className="bg-[var(--status-error)] hover:bg-[var(--status-error)]/90 text-white border-0">
+            <Button size="sm" variant="destructive" onClick={() => void handleConfirmDelete()} disabled={isDeletePending}>
               Delete
-            </ButtonLarge>
+            </Button>
           </DialogFooter>
         </DialogContent>
       </Dialog>
@@ -340,10 +338,10 @@ const DiscoveredRow: React.FC<DiscoveredRowProps> = ({ credential, onImport, has
           {isRepoSpecific ? credential.host : credential.username}
         </span>
       </div>
-      <ButtonSmall variant="ghost" onClick={onImport} className="gap-1 shrink-0">
+      <Button size="sm" variant="ghost" onClick={onImport} className="gap-1 shrink-0">
         <RiDownloadLine className="h-3 w-3" />
         Import
-      </ButtonSmall>
+      </Button>
     </div>
   );
 };