feat(03-02): install simple-git and create WorktreeManager adapter with CRUD

- Install simple-git dependency for git operations
- Create SimpleGitWorktreeManager class implementing WorktreeManager port
- Implement create(), remove(), list(), get() methods
- EventBus optional dependency injection for emitting worktree events
- Worktrees stored in .cw-worktrees directory

package.json

@@ -30,6 +30,8 @@
     "commander": "^12.1.0",
     "drizzle-orm": "^0.45.1",
     "execa": "^9.5.2",
+    "nanoid": "^5.1.6",
+    "simple-git": "^3.30.0",
     "zod": "^4.3.6"
   },
   "devDependencies": {