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/hooks/useSessionSidebarSections.ts

@@ -9,6 +9,10 @@ type ProjectItem = {
   path: string;
   label?: string;
   normalizedPath: string;
+  icon?: string;
+  color?: string;
+  iconImage?: { mime: string; updatedAt: number; source: 'custom' | 'auto' };
+  iconBackground?: string;
 };
 
 type ProjectSection = {
@@ -18,7 +22,6 @@ type ProjectSection = {
 
 type Args = {
   normalizedProjects: ProjectItem[];
-  activeProjectId: string | null;
   getSessionsForProject: (project: { normalizedPath: string }) => Session[];
   getArchivedSessionsForProject: (project: { normalizedPath: string }) => Session[];
   availableWorktreesByProject: Map<string, WorktreeMetadata[]>;
@@ -42,7 +45,6 @@ type Args = {
 export const useSessionSidebarSections = (args: Args) => {
   const {
     normalizedProjects,
-    activeProjectId,
     getSessionsForProject,
     getArchivedSessionsForProject,
     availableWorktreesByProject,
@@ -88,12 +90,8 @@ export const useSessionSidebarSections = (args: Args) => {
   ]);
 
   const visibleProjectSections = React.useMemo(() => {
-    if (projectSections.length === 0) {
-      return projectSections;
-    }
-    const active = projectSections.find((section) => section.project.id === activeProjectId);
-    return active ? [active] : [projectSections[0]];
-  }, [projectSections, activeProjectId]);
+    return projectSections;
+  }, [projectSections]);
 
   const groupSearchDataByGroup = React.useMemo(() => {
     const result = new WeakMap<SessionGroup, GroupSearchData>();