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/GitHeader.tsx

@@ -38,6 +38,8 @@ interface GitHeaderProps {
   onFetch: (remote: GitRemote) => void;
   onPull: (remote: GitRemote) => void;
   onPush: () => void;
+  onRemoveRemote: (remote: GitRemote) => void;
+  removingRemoteName: string | null;
   onCheckoutBranch: (branch: string) => void;
   onCreateBranch: (name: string, remote?: GitRemote) => Promise<void>;
   onRenameBranch?: (oldName: string, newName: string) => Promise<void>;
@@ -196,6 +198,8 @@ export const GitHeader: React.FC<GitHeaderProps> = ({
   onFetch,
   onPull,
   onPush,
+  onRemoveRemote,
+  removingRemoteName,
   onCheckoutBranch,
   onCreateBranch,
   onRenameBranch,
@@ -241,6 +245,8 @@ export const GitHeader: React.FC<GitHeaderProps> = ({
       onFetch={onFetch}
       onPull={onPull}
       onPush={onPush}
+      onRemoveRemote={onRemoveRemote}
+      removingRemoteName={removingRemoteName}
       disabled={!status}
       iconOnly={true}
       tooltipDelayMs={useTwoRowHeader ? 300 : 1000}