fix: address nitpick feedback from PR #423

## Security Fix (Command Injection)
- Use `execFile` with argument arrays instead of string interpolation
- Add `safeOpenInEditor` helper that properly handles `open -a` commands
- Validate that worktreePath is an absolute path before execution
- Prevents shell metacharacter injection attacks

## Shared Type Definition
- Move `EditorInfo` interface to `@automaker/types` package
- Server and UI now import from shared package to prevent drift
- Re-export from use-available-editors.ts for convenience

## Remove Unused Code
- Remove unused `defaultEditorName` prop from WorktreeActionsDropdown
- Remove prop from WorktreeTab component interface
- Remove useDefaultEditor hook usage from WorktreePanel
- Export new hooks from hooks/index.ts

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

libs/types/src/editor.ts

@@ -0,0 +1,13 @@
+/**
+ * Editor types for the "Open In" functionality
+ */
+
+/**
+ * Information about an available code editor
+ */
+export interface EditorInfo {
+  /** Display name of the editor (e.g., "VS Code", "Cursor") */
+  name: string;
+  /** CLI command or open command to launch the editor */
+  command: string;
+}

libs/types/src/index.ts

@@ -204,6 +204,9 @@ export type {
 // Port configuration
 export { STATIC_PORT, SERVER_PORT, RESERVED_PORTS } from './ports.js';
 
+// Editor types
+export type { EditorInfo } from './editor.js';
+
 // Ideation types
 export type {
   IdeaCategory,