Polish wording in agent feature description

[Chida82]

This PR improves the wording of the agent feature description to make it more grammatically correct, consistent, and natural in English, IMHO.

What changed

The previous text had a few grammar and style issues, including:

• singular/plural mismatches such as "KV cache mismatch are"
• unnatural phrasing such as "Displaying of generated text"
• less idiomatic expressions such as "switch session", "wanted shape", and "client-server way"
• missing punctuation after "However"
• a less natural sentence structure in the final paragraph