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/views/git/PullRequestSection.tsx

@@ -299,9 +299,8 @@ export const PullRequestSection: React.FC<{
   trackingBranch?: string;
   remotes?: GitRemote[];
   remoteBranches?: string[];
-  variant?: 'framed' | 'plain';
   onGeneratedDescription?: () => void;
-}> = ({ directory, branch, baseBranch, trackingBranch, remotes = [], remoteBranches = [], variant = 'framed', onGeneratedDescription }) => {
+}> = ({ directory, branch, baseBranch, trackingBranch, remotes = [], remoteBranches = [], onGeneratedDescription }) => {
   const { github } = useRuntimeAPIs();
   const githubAuthStatus = useGitHubAuthStore((state) => state.status);
   const githubAuthChecked = useGitHubAuthStore((state) => state.hasChecked);
@@ -1334,15 +1333,9 @@ export const PullRequestSection: React.FC<{
         ? RiGitClosePullRequestLine
         : RiGitPullRequestLine;
 
-  const containerClassName =
-    variant === 'framed'
-      ? 'rounded-xl border border-border/60 bg-transparent overflow-hidden'
-      : 'border-0 bg-transparent rounded-none';
-  const headerClassName =
-    variant === 'framed'
-      ? 'px-3 py-2 border-b border-border/40 flex flex-col gap-1'
-      : 'px-0 py-3 border-b border-border/40 flex flex-col gap-1';
-  const bodyClassName = variant === 'framed' ? 'flex flex-col gap-3 p-3' : 'flex flex-col gap-3 py-3';
+  const containerClassName = 'border-0 bg-transparent rounded-none';
+  const headerClassName = 'px-0 py-3 border-b border-border/40 flex flex-col gap-1';
+  const bodyClassName = 'flex flex-col gap-3 py-3';
 
   return (
     <section className={containerClassName}>
@@ -1382,7 +1375,7 @@ export const PullRequestSection: React.FC<{
             {hasMultipleRemotes ? (
               <DropdownMenu>
                 <DropdownMenuTrigger asChild>
-                  <Button variant="ghost" size="sm" className="h-6 px-2 gap-1">
+                  <Button variant="ghost" size="xs" className="gap-1">
                     <span className="typography-micro">{selectedRemote?.name}</span>
                     <RiArrowDownSLine className="size-3" />
                   </Button>
@@ -1693,7 +1686,7 @@ export const PullRequestSection: React.FC<{
                     </div>
                   </div>
                   {repoUrl ? (
-                    <Button variant="outline" size="sm" className="h-7 px-2 py-0" asChild>
+                    <Button variant="outline" size="sm" asChild>
                       <a href={repoUrl} target="_blank" rel="noopener noreferrer">
                         <RiExternalLinkLine className="size-4" />
                         Repo
@@ -1863,7 +1856,6 @@ export const PullRequestSection: React.FC<{
                   <Button
                     variant="outline"
                     size="sm"
-                    className="h-7 px-2 py-0"
                     onClick={generateDescription}
                     disabled={isGenerating || isCreating}
                   >
@@ -1873,7 +1865,7 @@ export const PullRequestSection: React.FC<{
                   <div className="flex-1" />
                   <Button
                     size="sm"
-                    className="h-7 min-w-[7.5rem] justify-center gap-2 px-2 py-0"
+                    className="min-w-[7.5rem] justify-center gap-2"
                     onClick={createPr}
                     disabled={isCreating || !isConnected || !targetBaseBranch.trim() || targetBaseBranch.trim() === branch}
                   >