fix(do): isolate stop hook by task_id to prevent concurrent task interference

When running multiple do tasks concurrently in worktrees, the stop hook
would scan all do.*.local.md files and block exit for unrelated tasks.

Changes:
- setup-do.sh: export DO_TASK_ID for hook environment
- stop-hook.sh: filter state files by DO_TASK_ID when set, fallback to
  scanning all files for backward compatibility

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

skills/do/hooks/stop-hook.sh

@@ -29,7 +29,16 @@ project_dir="${CLAUDE_PROJECT_DIR:-$PWD}"
 state_dir="${project_dir}/.claude"
 
 shopt -s nullglob
-state_files=("${state_dir}"/do.*.local.md)
+if [ -n "${DO_TASK_ID:-}" ]; then
+	candidate="${state_dir}/do.${DO_TASK_ID}.local.md"
+	if [ -f "$candidate" ]; then
+		state_files=("$candidate")
+	else
+		state_files=()
+	fi
+else
+	state_files=("${state_dir}"/do.*.local.md)
+fi
 shopt -u nullglob
 
 if [ ${#state_files[@]} -eq 0 ]; then

skills/do/scripts/setup-do.sh

@@ -112,3 +112,4 @@ echo "Initialized: $state_file"
 echo "task_id: $task_id"
 echo "phase: 1/$max_phases ($phase_name)"
 echo "completion_promise: $completion_promise"
+echo "export DO_TASK_ID=$task_id"