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/message/TextSelectionMenu.tsx

@@ -24,6 +24,12 @@ interface SelectionPayload {
 
 const DESKTOP_MENU_SIDE_MARGIN_PX = 8;
 const DESKTOP_MENU_FALLBACK_WIDTH_PX = 280;
+const BLOCK_TAGS = new Set([
+  'address', 'article', 'aside', 'blockquote', 'dd', 'div', 'dl', 'dt',
+  'fieldset', 'figcaption', 'figure', 'footer', 'form', 'h1', 'h2', 'h3',
+  'h4', 'h5', 'h6', 'header', 'hr', 'li', 'main', 'nav', 'ol', 'p', 'pre',
+  'section', 'table', 'ul',
+]);
 
 const normalizeLineBreaks = (value: string): string => value.replace(/\r\n?/g, '\n');
 
@@ -103,6 +109,11 @@ const renderBlockMarkdownNode = (node: Node): string => {
     return `\`\`\`${language}\n${code}\n\`\`\``;
   }
 
+  if (tag === 'code') {
+    const code = normalizeLineBreaks(element.textContent || '').trim();
+    return code ? `\`${code.replace(/`/g, '\\`')}\`` : '';
+  }
+
   if (tag === 'ul') return renderListMarkdown(element, false);
   if (tag === 'ol') return renderListMarkdown(element, true);
 
@@ -137,8 +148,34 @@ const renderBlockMarkdownNode = (node: Node): string => {
   return trimSelectionValue(Array.from(element.childNodes).map((child) => renderInlineMarkdownNode(child)).join(''));
 };
 
+const isInlineSelectionFragment = (fragment: DocumentFragment): boolean => {
+  return Array.from(fragment.childNodes).every((node) => {
+    if (node.nodeType === Node.TEXT_NODE) {
+      return true;
+    }
+    if (node.nodeType !== Node.ELEMENT_NODE) {
+      return true;
+    }
+
+    const element = node as HTMLElement;
+    return !BLOCK_TAGS.has(element.tagName.toLowerCase());
+  });
+};
+
 const rangeToMarkdown = (range: Range, plainText: string): string => {
   const fragment = range.cloneContents();
+
+  if (isInlineSelectionFragment(fragment)) {
+    const inlineMarkdown = trimSelectionValue(
+      Array.from(fragment.childNodes)
+        .map((node) => renderInlineMarkdownNode(node))
+        .join('')
+    );
+    if (inlineMarkdown) {
+      return inlineMarkdown;
+    }
+  }
+
   const markdown = Array.from(fragment.childNodes)
     .map((node) => renderBlockMarkdownNode(node))
     .filter((value) => value.length > 0)
@@ -436,6 +473,8 @@ export const TextSelectionMenu: React.FC<TextSelectionMenuProps> = ({ containerR
         )}
         style={{
           paddingBottom: 'calc(0.5rem + env(safe-area-inset-bottom, 0px))',
+          backdropFilter: 'blur(28px)',
+          WebkitBackdropFilter: 'blur(28px)',
         }}
       >
         <button
@@ -507,6 +546,10 @@ export const TextSelectionMenu: React.FC<TextSelectionMenuProps> = ({ containerR
           'transition-[opacity,transform] duration-200 ease-out will-change-[opacity,transform]',
           isOpening ? 'opacity-0 translate-y-[4px]' : 'opacity-100 translate-y-0'
         )}
+        style={{
+          backdropFilter: 'blur(28px)',
+          WebkitBackdropFilter: 'blur(28px)',
+        }}
       >
         <button
           onClick={handleAddToChat}