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/lib/opencode/client.ts

@@ -129,6 +129,7 @@ export type DirectorySwitchResult = {
 };
 
 const normalizeFsPath = (path: string): string => path.replace(/\\/g, "/");
+const FS_LIST_CACHE_TTL_MS = 400;
 
 const getDesktopFilesApi = (): FilesAPI | null => {
   if (typeof window === "undefined") {
@@ -161,6 +162,8 @@ class OpencodeService {
   private globalSseStaleDeltas: Set<string> = new Set();
   private globalSseFlushTimer: ReturnType<typeof setTimeout> | null = null;
   private globalSseLastFlushAt = 0;
+  private listDirectoryInFlight: Map<string, Promise<FilesystemEntry[]>> = new Map();
+  private listDirectoryCache: Map<string, { entries: FilesystemEntry[]; expiresAt: number }> = new Map();
 
   constructor(baseUrl: string = DEFAULT_BASE_URL) {
     const desktopBase = resolveDesktopBaseUrl();
@@ -2030,6 +2033,20 @@ class OpencodeService {
   }
 
   async listLocalDirectory(directoryPath: string | null | undefined, options?: { respectGitignore?: boolean }): Promise<FilesystemEntry[]> {
+    const normalizedDirectoryPath = typeof directoryPath === 'string' ? normalizeFsPath(directoryPath.trim()) : '';
+    const cacheKey = `${normalizedDirectoryPath}|${options?.respectGitignore ? '1' : '0'}`;
+    const now = Date.now();
+    const cached = this.listDirectoryCache.get(cacheKey);
+    if (cached && cached.expiresAt > now) {
+      return cached.entries;
+    }
+
+    const inFlight = this.listDirectoryInFlight.get(cacheKey);
+    if (inFlight) {
+      return inFlight;
+    }
+
+    const task = (async () => {
     const desktopFiles = getDesktopFilesApi();
     if (desktopFiles) {
       try {
@@ -2037,13 +2054,18 @@ class OpencodeService {
         if (!result || !Array.isArray(result.entries)) {
           return [];
         }
-        return result.entries.map<FilesystemEntry>((entry) => ({
+        const entries = result.entries.map<FilesystemEntry>((entry) => ({
           name: entry.name,
           path: normalizeFsPath(entry.path),
           isDirectory: !!entry.isDirectory,
           isFile: !entry.isDirectory,
           isSymbolicLink: false,
         }));
+        this.listDirectoryCache.set(cacheKey, {
+          entries,
+          expiresAt: Date.now() + FS_LIST_CACHE_TTL_MS,
+        });
+        return entries;
       } catch (error) {
         console.error('Failed to list directory contents:', error);
         throw error;
@@ -2071,11 +2093,25 @@ class OpencodeService {
         return [];
       }
 
-      return result.entries as FilesystemEntry[];
+      const entries = result.entries as FilesystemEntry[];
+      this.listDirectoryCache.set(cacheKey, {
+        entries,
+        expiresAt: Date.now() + FS_LIST_CACHE_TTL_MS,
+      });
+      return entries;
     } catch (error) {
       console.error('Failed to list directory contents:', error);
       throw error;
     }
+    })();
+
+    const trackedTask = task.finally(() => {
+      if (this.listDirectoryInFlight.get(cacheKey) === trackedTask) {
+        this.listDirectoryInFlight.delete(cacheKey);
+      }
+    });
+    this.listDirectoryInFlight.set(cacheKey, trackedTask);
+    return trackedTask;
   }
 
   async searchFiles(