fix: update agent count display in PlanningFlow

[ASPrimeK]

Features

• Fixed an issue where the agents_description list was passed instead of its length (len()) in the system prompt.

Feature Docs

Influence

• Ensures the prompt displays the correct number of agents instead of dumping the raw list object into the sentence.

Result

• The system prompt now correctly displays "Now we have 2 agents..." instead of the entire list string.

Other