feat: add default IDE setting and multi-editor support with icons

Add comprehensive editor detection and selection system that allows users
to configure their preferred IDE for opening branches and worktrees.

## Server-side Changes

- Add `/api/worktree/available-editors` endpoint to detect installed editors
- Support detection via CLI commands (cursor, code, zed, subl, etc.)
- Support detection via macOS app bundles in /Applications and ~/Applications
- Detect editors: Cursor, VS Code, Zed, Sublime Text, Windsurf, Trae,
  Rider, WebStorm, Xcode, Android Studio, Antigravity, and file managers

## UI Changes

### Editor Icons
- Add new `editor-icons.tsx` with SVG icons for all supported editors
- Icons: Cursor, VS Code, Zed, Sublime Text, Windsurf, Trae, Rider,
  WebStorm, Xcode, Android Studio, Antigravity, Finder
- `getEditorIcon()` helper maps editor commands to appropriate icons

### Default IDE Setting
- Add "Default IDE" selector in Settings > Account section
- Options: Auto-detect (Cursor > VS Code > first available) or explicit choice
- Setting persists via `defaultEditorCommand` in global settings

### Worktree Dropdown Improvements
- Implement split-button UX for "Open In" action
- Click main area: opens directly in default IDE (single click)
- Click chevron: shows submenu with other editors + Copy Path
- Each editor shows with its branded icon

## Type & Store Changes

- Add `defaultEditorCommand: string | null` to GlobalSettings
- Add to app-store with `setDefaultEditorCommand` action
- Add to SETTINGS_FIELDS_TO_SYNC for persistence
- Add `useAvailableEditors` hook for fetching detected editors

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/ui/src/store/app-store.ts

@@ -585,6 +585,9 @@ export interface AppState {
   // MCP Servers
   mcpServers: MCPServerConfig[]; // List of configured MCP servers for agent use
 
+  // Editor Configuration
+  defaultEditorCommand: string | null; // Default editor for "Open In" action
+
   // Skills Configuration
   enableSkills: boolean; // Enable Skills functionality (loads from .claude/skills/ directories)
   skillsSources: Array<'user' | 'project'>; // Which directories to load Skills from
@@ -958,6 +961,9 @@ export interface AppActions {
   setAutoLoadClaudeMd: (enabled: boolean) => Promise<void>;
   setSkipSandboxWarning: (skip: boolean) => Promise<void>;
 
+  // Editor Configuration actions
+  setDefaultEditorCommand: (command: string | null) => void;
+
   // Prompt Customization actions
   setPromptCustomization: (customization: PromptCustomization) => Promise<void>;
 
@@ -1196,6 +1202,7 @@ const initialState: AppState = {
   autoLoadClaudeMd: false, // Default to disabled (user must opt-in)
   skipSandboxWarning: false, // Default to disabled (show sandbox warning dialog)
   mcpServers: [], // No MCP servers configured by default
+  defaultEditorCommand: null, // Auto-detect: Cursor > VS Code > first available
   enableSkills: true, // Skills enabled by default
   skillsSources: ['user', 'project'] as Array<'user' | 'project'>, // Load from both sources by default
   enableSubagents: true, // Subagents enabled by default
@@ -1959,6 +1966,9 @@ export const useAppStore = create<AppState & AppActions>()((set, get) => ({
       set({ skipSandboxWarning: previous });
     }
   },
+
+  // Editor Configuration actions
+  setDefaultEditorCommand: (command) => set({ defaultEditorCommand: command }),
   // Prompt Customization actions
   setPromptCustomization: async (customization) => {
     set({ promptCustomization: customization });