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/sections/projects/ProjectActionsSection.tsx

@@ -7,7 +7,7 @@ import {
   RiInformationLine,
   RiPlayLine,
 } from '@remixicon/react';
-import { ButtonSmall } from '@/components/ui/button-small';
+import { Button } from '@/components/ui/button';
 import { Checkbox } from '@/components/ui/checkbox';
 import {
   Collapsible,
@@ -198,10 +198,10 @@ export const ProjectActionsSection: React.FC<ProjectActionsSectionProps> = ({ pr
           <h3 className="typography-ui-header font-medium text-foreground">Actions</h3>
           <p className="typography-meta text-muted-foreground">Per-project commands shown in header next to project name.</p>
         </div>
-        <ButtonSmall type="button" variant="outline" size="xs" className="!font-normal" onClick={handleAddAction}>
+        <Button type="button" variant="outline" size="xs" className="!font-normal" onClick={handleAddAction}>
           <RiAddLine className="h-3.5 w-3.5" />
           Add action
-        </ButtonSmall>
+        </Button>
       </div>
 
       <section className="pb-2 pt-0 space-y-2">
@@ -248,7 +248,7 @@ export const ProjectActionsSection: React.FC<ProjectActionsSectionProps> = ({ pr
                       </div>
                     </CollapsibleTrigger>
 
-                    <ButtonSmall
+                    <Button
                       type="button"
                       variant="ghost"
                       size="xs"
@@ -256,7 +256,7 @@ export const ProjectActionsSection: React.FC<ProjectActionsSectionProps> = ({ pr
                       onClick={() => handleRemoveAction(action.id)}
                     >
                       <RiDeleteBinLine className="h-3.5 w-3.5" />
-                    </ButtonSmall>
+                    </Button>
                   </div>
 
                   <CollapsibleContent className="pt-1.5">
@@ -418,7 +418,7 @@ export const ProjectActionsSection: React.FC<ProjectActionsSectionProps> = ({ pr
           {validationError ? (
             <p className="typography-meta mb-2 text-[var(--status-warning)]">{validationError}</p>
           ) : null}
-          <ButtonSmall
+          <Button
             type="button"
             size="xs"
             className="!font-normal"
@@ -426,7 +426,7 @@ export const ProjectActionsSection: React.FC<ProjectActionsSectionProps> = ({ pr
             disabled={!canSave}
           >
             {isSaving ? 'Saving...' : 'Save Actions'}
-          </ButtonSmall>
+          </Button>
         </div>
       </section>
     </div>