feat: Add sidebar style options to appearance settings

- Introduced a new section in the Appearance settings to allow users to choose between 'unified' and 'discord' sidebar layouts.
- Updated the app state and settings migration to include the new sidebarStyle property.
- Enhanced the UI to reflect the selected sidebar style with appropriate visual feedback.
- Ensured synchronization of sidebar style settings across the application.

libs/types/src/index.ts

@@ -145,6 +145,7 @@ export { DEFAULT_PROMPT_CUSTOMIZATION } from './prompts.js';
 // Settings types and constants
 export type {
   ThemeMode,
+  SidebarStyle,
   PlanningMode,
   ThinkingLevel,
   ServerLogLevel,

libs/types/src/settings.ts

@@ -78,6 +78,14 @@ export type ServerLogLevel = 'error' | 'warn' | 'info' | 'debug';
 /** ThinkingLevel - Extended thinking levels for Claude models (reasoning intensity) */
 export type ThinkingLevel = 'none' | 'low' | 'medium' | 'high' | 'ultrathink';
 
+/**
+ * SidebarStyle - Sidebar layout style options
+ *
+ * - 'unified': Single sidebar with integrated project dropdown (default, modern)
+ * - 'discord': Two sidebars - narrow project switcher + expandable navigation sidebar (classic)
+ */
+export type SidebarStyle = 'unified' | 'discord';
+
 /**
  * Thinking token budget mapping based on Claude SDK documentation.
  * @see https://docs.anthropic.com/en/docs/build-with-claude/extended-thinking
@@ -836,6 +844,8 @@ export interface GlobalSettings {
   // UI State Preferences
   /** Whether sidebar is currently open */
   sidebarOpen: boolean;
+  /** Sidebar layout style ('unified' = modern single sidebar, 'discord' = classic two-sidebar layout) */
+  sidebarStyle: SidebarStyle;
   /** Whether chat history panel is open */
   chatHistoryOpen: boolean;
 
@@ -1310,6 +1320,7 @@ export const DEFAULT_GLOBAL_SETTINGS: GlobalSettings = {
   skipClaudeSetup: false,
   theme: 'dark',
   sidebarOpen: true,
+  sidebarStyle: 'unified',
   chatHistoryOpen: false,
   maxConcurrency: DEFAULT_MAX_CONCURRENCY,
   defaultSkipTests: true,