Guide Box and Notion agents to stop retrying unavailable tools

[william-openai]

Summary

• add a Box skill guardrail that treats Tool <name> not found as terminal for that tool during the current task
• add the same Notion guardrail to all four Notion entry skills
• direct Notion agents to use search and fetch when those available fallbacks are sufficient
• normalize Notion skill, example, reference, and eval-rubric mentions of the special-cased live tools from notion-search / notion-fetch to search / fetch