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/useProjectSessionSelection.ts

@@ -15,7 +15,6 @@ type Args = {
   setActiveSessionByProject: React.Dispatch<React.SetStateAction<Map<string, string>>>;
   currentSessionId: string | null;
   handleSessionSelect: (sessionId: string, sessionDirectory: string | null, isMissingDirectory: boolean, projectId?: string | null) => void;
-  isVSCode: boolean;
   newSessionDraftOpen: boolean;
   mobileVariant: boolean;
   openNewSessionDraft: (options?: { directoryOverride?: string | null }) => void;
@@ -33,7 +32,6 @@ export const useProjectSessionSelection = (args: Args): { currentSessionDirector
     setActiveSessionByProject,
     currentSessionId,
     handleSessionSelect,
-    isVSCode,
     newSessionDraftOpen,
     mobileVariant,
     openNewSessionDraft,
@@ -84,18 +82,13 @@ export const useProjectSessionSelection = (args: Args): { currentSessionDirector
   }, [projectSections]);
 
   const previousActiveProjectRef = React.useRef<string | null>(null);
-  const lastSeenActiveProjectRef = React.useRef<string | null>(null);
 
   React.useLayoutEffect(() => {
     if (!activeProjectId) {
       return;
     }
 
-    const previousSeenProjectId = lastSeenActiveProjectRef.current;
-    const isProjectSwitch = Boolean(previousSeenProjectId && previousSeenProjectId !== activeProjectId);
-    lastSeenActiveProjectRef.current = activeProjectId;
-
-    if (newSessionDraftOpen && (isVSCode || !isProjectSwitch)) {
+    if (newSessionDraftOpen) {
       return;
     }
 
@@ -146,7 +139,6 @@ export const useProjectSessionSelection = (args: Args): { currentSessionDirector
     activeSessionByProject,
     currentSessionId,
     handleSessionSelect,
-    isVSCode,
     newSessionDraftOpen,
     mobileVariant,
     openNewSessionDraft,