Add text-based Planfix sell task tool

[popstas]

Summary

• rename the identifier-based sell task implementation to planfix_create_sell_task_ids and expose it as a standalone tool
• add a new planfix_create_sell_task tool that resolves contact, agency, and lead task IDs from string inputs before delegating to the ID-based helper
• update documentation, tests, and server registration to cover the new tools and behaviours

Testing

• npm run format
• npm run test-full

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https://chatgpt.com/codex/tasks/task_e_68df8ed001b4832c8b3288263f412b50