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/components/views/board-view/worktree-panel/hooks/use-available-editors.ts

@@ -0,0 +1,46 @@
+import { useState, useEffect, useCallback } from 'react';
+import { createLogger } from '@automaker/utils/logger';
+import { getElectronAPI } from '@/lib/electron';
+
+const logger = createLogger('AvailableEditors');
+
+export interface EditorInfo {
+  name: string;
+  command: string;
+}
+
+export function useAvailableEditors() {
+  const [editors, setEditors] = useState<EditorInfo[]>([]);
+  const [isLoading, setIsLoading] = useState(true);
+
+  const fetchAvailableEditors = useCallback(async () => {
+    try {
+      const api = getElectronAPI();
+      if (!api?.worktree?.getAvailableEditors) {
+        setIsLoading(false);
+        return;
+      }
+      const result = await api.worktree.getAvailableEditors();
+      if (result.success && result.result?.editors) {
+        setEditors(result.result.editors);
+      }
+    } catch (error) {
+      logger.error('Failed to fetch available editors:', error);
+    } finally {
+      setIsLoading(false);
+    }
+  }, []);
+
+  useEffect(() => {
+    fetchAvailableEditors();
+  }, [fetchAvailableEditors]);
+
+  return {
+    editors,
+    isLoading,
+    // Convenience property: has multiple editors (for deciding whether to show submenu)
+    hasMultipleEditors: editors.length > 1,
+    // The first editor is the "default" one
+    defaultEditor: editors[0] ?? null,
+  };
+}

apps/ui/src/components/views/board-view/worktree-panel/hooks/use-worktree-actions.ts

@@ -125,14 +125,14 @@ export function useWorktreeActions({ fetchWorktrees, fetchBranches }: UseWorktre
     [isPushing, fetchBranches, fetchWorktrees]
   );
 
-  const handleOpenInEditor = useCallback(async (worktree: WorktreeInfo) => {
+  const handleOpenInEditor = useCallback(async (worktree: WorktreeInfo, editorCommand?: string) => {
     try {
       const api = getElectronAPI();
       if (!api?.worktree?.openInEditor) {
         logger.warn('Open in editor API not available');
         return;
       }
-      const result = await api.worktree.openInEditor(worktree.path);
+      const result = await api.worktree.openInEditor(worktree.path, editorCommand);
       if (result.success && result.result) {
         toast.success(result.result.message);
       } else if (result.error) {