docs(notion-writer): fix plan — circular import, columns loop, error hint

Pre-flight review fixes: lazy import in md_translate to break the
notion_writer<->md_translate cycle; clean columns state machine; markdown
deletion hint in explain_api_error.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/superpowers/plans/2026-06-27-notion-writer-cli-enhancements.md

@@ -674,7 +674,8 @@ from __future__ import annotations
 import re
 from typing import List
 
-from notion_writer import extract_notion_id, format_id_with_dashes
+# NOTE: `notion_writer` is imported lazily inside _translate_mentions to avoid
+# a circular import (notion_writer imports this module at its top level).
 
 # Skill alert type -> (emoji, Notion enhanced-markdown background color)
 CALLOUT_MAP = {
@@ -689,6 +690,8 @@ _MENTION_RE = re.compile(r'@\[([^\]]+)\]\(([^)\s]+)\)')
 
 
 def _translate_mentions(text: str) -> str:
+    from notion_writer import extract_notion_id, format_id_with_dashes  # lazy: breaks import cycle
+
     def repl(m: "re.Match") -> str:
         title, target = m.group(1), m.group(2)
         page_id = extract_notion_id(target)