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/session/sidebar/utils.tsx

@@ -45,6 +45,34 @@ export const formatSessionDateLabel = (updatedMs: number): string => {
   return formatDateLabel(updatedMs);
 };
 
+export const formatSessionCompactDateLabel = (updatedMs: number): string => {
+  const diff = Math.max(0, Date.now() - updatedMs);
+
+  const minute = 60_000;
+  const hour = 60 * minute;
+  const day = 24 * hour;
+  const week = 7 * day;
+  const month = 30 * day;
+  const year = 365 * day;
+
+  if (diff < hour) {
+    return `${Math.max(1, Math.floor(diff / minute))}m`;
+  }
+  if (diff < day) {
+    return `${Math.floor(diff / hour)}h`;
+  }
+  if (diff < week) {
+    return `${Math.floor(diff / day)}d`;
+  }
+  if (diff < 5 * week) {
+    return `${Math.floor(diff / week)}w`;
+  }
+  if (diff < year) {
+    return `${Math.floor(diff / month)}mo`;
+  }
+  return `${Math.floor(diff / year)}y`;
+};
+
 export const normalizePath = (value?: string | null) => {
   if (!value) {
     return null;