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/views/git/ChangesSection.tsx

@@ -28,7 +28,6 @@ interface ChangesSectionProps {
   onViewDiff: (path: string) => void;
   onRevertFile: (path: string) => void;
   isRevertingAll?: boolean;
-  variant?: 'framed' | 'plain';
   maxListHeightClassName?: string;
   onVisiblePathsChange?: (paths: string[]) => void;
 }
@@ -48,7 +47,6 @@ export const ChangesSection: React.FC<ChangesSectionProps> = ({
   onViewDiff,
   onRevertFile,
   isRevertingAll = false,
-  variant = 'framed',
   maxListHeightClassName,
   onVisiblePathsChange,
 }) => {
@@ -92,19 +90,10 @@ export const ChangesSection: React.FC<ChangesSectionProps> = ({
     onVisiblePathsChange(virtualRows.map((row) => changeEntries[row.index]?.path).filter((value): value is string => Boolean(value)));
   }, [changeEntries, onVisiblePathsChange, shouldVirtualize, totalCount, virtualRows]);
 
-  const containerClassName =
-    variant === 'framed'
-      ? 'flex flex-col rounded-xl border border-border/60 bg-background/70'
-      : 'flex flex-col flex-1 min-h-0';
-  const headerClassName =
-    variant === 'framed'
-      ? 'flex items-center justify-between gap-2 px-3 py-2 border-b border-border/40'
-      : 'flex items-center justify-between gap-2 px-0 py-3 border-b border-border/40';
-  const scrollOuterClassName =
-    variant === 'framed'
-      ? 'flex-1 min-h-0 max-h-[30vh]'
-      : `flex-1 min-h-0 pr-0 ${maxListHeightClassName ?? ''}`.trim();
-  const rowPaddingClassName = variant === 'plain' ? 'pl-0 pr-2' : 'px-3';
+  const containerClassName = 'flex flex-col flex-1 min-h-0';
+  const headerClassName = 'flex items-center justify-between gap-2 px-0 py-3 border-b border-border/40';
+  const scrollOuterClassName = `flex-1 min-h-0 pr-0 ${maxListHeightClassName ?? ''}`.trim();
+  const rowPaddingClassName = 'pl-0 pr-2';
 
   const handleConfirmRevertAll = React.useCallback(async () => {
     if (!onRevertAll || isRevertingAll || changeEntries.length === 0) {
@@ -144,12 +133,11 @@ export const ChangesSection: React.FC<ChangesSectionProps> = ({
               </button>
             ) : null}
           </div>
-          <div className={cn('flex items-center gap-2', variant === 'plain' && 'pr-1')}>
+          <div className="flex items-center gap-2 pr-1">
             {totalCount > 0 && onRevertAll ? (
               <Button
-                variant="ghost"
-                size="sm"
-                className="h-6 px-2 text-xs text-[var(--status-error)] hover:text-[var(--status-error)]"
+                variant="destructive"
+                size="xs"
                 onClick={() => setConfirmRevertAllOpen(true)}
                 disabled={isRevertingAll}
               >
@@ -237,10 +225,10 @@ export const ChangesSection: React.FC<ChangesSectionProps> = ({
             </DialogDescription>
           </DialogHeader>
           <DialogFooter>
-            <Button variant="outline" onClick={() => setConfirmRevertAllOpen(false)} disabled={isRevertingAll}>
+            <Button variant="outline" size="sm" onClick={() => setConfirmRevertAllOpen(false)} disabled={isRevertingAll}>
               Cancel
             </Button>
-            <Button variant="destructive" onClick={() => void handleConfirmRevertAll()} disabled={isRevertingAll}>
+            <Button variant="destructive" size="sm" onClick={() => void handleConfirmRevertAll()} disabled={isRevertingAll}>
               {isRevertingAll ? 'Reverting...' : 'Revert all'}
             </Button>
           </DialogFooter>