feat(HAI-034): use humanized worktree names instead of task-ID-based directories

- Add worktree-names module with adjective-animal name generator (generateWorktreeName)
- Update executor to assign humanized random worktree names and support dependency worktree reuse
- Remove task-ID fallback paths from merger and store; add shared worktree cleanup via findWorktreeUser
- Remove worktree pool module and related scheduler/integration tests
- Update dashboard worktree label tests and add JSDoc documentation for worktree naming

packages/core/src/store.ts

@@ -468,7 +468,7 @@ export class TaskStore extends EventEmitter<TaskStoreEvents> {
       }
 
       const branch = `hai/${id.toLowerCase()}`;
-      const worktreePath = task.worktree || join(this.rootDir, ".worktrees", id);
+      const worktreePath = task.worktree;
       const result: MergeResult = {
         task,
         branch,
@@ -519,7 +519,7 @@ export class TaskStore extends EventEmitter<TaskStoreEvents> {
       }
 
       // 3. Remove worktree
-      if (existsSync(worktreePath)) {
+      if (worktreePath && existsSync(worktreePath)) {
         try {
           execSync(`git worktree remove "${worktreePath}" --force`, {
             cwd: this.rootDir,