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/chat/ChatEmptyState.tsx

@@ -1,12 +1,7 @@
 import React from 'react';
-import { RiGitBranchLine } from '@remixicon/react';
-
 import { OpenChamberLogo } from '@/components/ui/OpenChamberLogo';
 import { TextLoop } from '@/components/ui/TextLoop';
 import { useThemeSystem } from '@/contexts/useThemeSystem';
-import { useRuntimeAPIs } from '@/hooks/useRuntimeAPIs';
-import { useEffectiveDirectory } from '@/hooks/useEffectiveDirectory';
-import { useGitStatus, useGitStore } from '@/stores/useGitStore';
 
 const phrases = [
     "Fix the failing tests",
@@ -27,51 +22,15 @@ const phrases = [
     "Add type definitions",
 ];
 
-interface ChatEmptyStateProps {
-    showDraftContext?: boolean;
-}
-
-const ChatEmptyState: React.FC<ChatEmptyStateProps> = ({
-    showDraftContext = false,
-}) => {
+const ChatEmptyState: React.FC = () => {
     const { currentTheme } = useThemeSystem();
-    const { git } = useRuntimeAPIs();
-    const effectiveDirectory = useEffectiveDirectory();
-    const { setActiveDirectory, fetchStatus } = useGitStore();
-    const gitStatus = useGitStatus(effectiveDirectory ?? null);
 
     // Use theme's muted foreground for secondary text
     const textColor = currentTheme?.colors?.surface?.mutedForeground || 'var(--muted-foreground)';
-    const branchName = typeof gitStatus?.current === 'string' && gitStatus.current.trim().length > 0
-        ? gitStatus.current.trim()
-        : null;
-
-    React.useEffect(() => {
-        if (!showDraftContext || !effectiveDirectory) {
-            return;
-        }
-
-        setActiveDirectory(effectiveDirectory);
-
-        const state = useGitStore.getState().directories.get(effectiveDirectory);
-        if (!state?.status && state?.isGitRepo !== false) {
-            void fetchStatus(effectiveDirectory, git, { silent: true });
-        }
-    }, [effectiveDirectory, fetchStatus, git, setActiveDirectory, showDraftContext]);
 
     return (
         <div className="flex flex-col items-center justify-center min-h-full w-full gap-6">
             <OpenChamberLogo width={140} height={140} className="opacity-20" isAnimated />
-            {showDraftContext && (
-                <div className="max-w-[calc(100%-2rem)] flex flex-col items-center gap-1">
-                    {branchName && (
-                        <div className="inline-flex items-center gap-1 text-body-md" style={{ color: textColor }}>
-                            <RiGitBranchLine className="h-4 w-4 shrink-0" />
-                            <span className="overflow-hidden whitespace-nowrap" title={branchName}>{branchName}</span>
-                        </div>
-                    )}
-                </div>
-            )}
             <TextLoop
                 className="text-body-md"
                 interval={4}