Shorten sequentialthinking tool description

[pntech20]

Summary

• Shorten the sequentialthinking tool description from about 2,780 characters to 782 characters.
• Keep detailed argument guidance in the Zod input schema descriptions.
• Avoid OpenAI tool-description limit failures like the one reported in sequentialthinking tool description beyond OpenAI length limitation #799.

Fixes #799

Verification

• Verified toolDescription length is 782 characters, below the 1,024-character limit from the issue.
• npm --workspace src/sequentialthinking run build
• npm --workspace src/sequentialthinking test