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/MarkdownRenderer.tsx

@@ -971,12 +971,14 @@ const useFileReferenceInteractions = ({
   readFile,
   editor,
   preferRuntimeEditor,
+  deferValidationUntilIdle = false,
 }: {
   containerRef: React.RefObject<HTMLDivElement | null>;
   effectiveDirectory: string;
   readFile?: (path: string) => Promise<{ content: string; path: string }>;
   editor?: EditorAPI;
   preferRuntimeEditor?: boolean;
+  deferValidationUntilIdle?: boolean;
 }) => {
   const validationCacheRef = React.useRef<Map<string, boolean>>(new Map());
   const inFlightValidationsRef = React.useRef<Map<string, Promise<boolean>>>(new Map());
@@ -1048,6 +1050,9 @@ const useFileReferenceInteractions = ({
     };
 
     const runValidationSweep = async (paths: string[], expectedPassID: number) => {
+      if (deferValidationUntilIdle) {
+        return;
+      }
       if (isValidationSweepRunningRef.current || paths.length === 0) {
         return;
       }
@@ -1208,9 +1213,13 @@ const useFileReferenceInteractions = ({
       annotationDebounceRef.current = window.setTimeout(() => {
         annotationDebounceRef.current = null;
         void annotateFileLinks();
-      }, 120);
+      }, deferValidationUntilIdle ? 280 : 120);
+    });
+    observer.observe(container, {
+      childList: true,
+      subtree: true,
+      ...(deferValidationUntilIdle ? {} : { characterData: true }),
     });
-    observer.observe(container, { childList: true, subtree: true, characterData: true });
 
     container.addEventListener('click', handleClick);
     container.addEventListener('keydown', handleKeyDown);
@@ -1226,7 +1235,7 @@ const useFileReferenceInteractions = ({
       container.removeEventListener('click', handleClick);
       container.removeEventListener('keydown', handleKeyDown);
     };
-  }, [containerRef, editor, effectiveDirectory, preferRuntimeEditor, readFile]);
+  }, [containerRef, deferValidationUntilIdle, editor, effectiveDirectory, preferRuntimeEditor, readFile]);
 };
 
 const useMermaidInlineInteractions = ({
@@ -1345,6 +1354,7 @@ export const MarkdownRenderer: React.FC<MarkdownRendererProps> = ({
     readFile: files.readFile,
     editor,
     preferRuntimeEditor: runtime.isVSCode,
+    deferValidationUntilIdle: isStreaming,
   });
 
   const shikiThemes = useMarkdownShikiThemes();
@@ -1358,10 +1368,7 @@ export const MarkdownRenderer: React.FC<MarkdownRendererProps> = ({
       ? 'streamdown-content streamdown-reasoning'
       : 'streamdown-content';
 
-  const streamdownAnimated = React.useMemo(
-    () => ({ animation: 'blurIn' as const, duration: 150, easing: 'ease-out' }),
-    [],
-  );
+  const streamdownAnimated = undefined;
 
   const markdownContent = (
     <div className={cn('break-words w-full min-w-0', className)} ref={streamdownContainerRef}>