`agent_card_builder` doesn't use correct grammar

[holtskinner]

Describe the bug

When using to_a2a() the autogenerated AgentCard substitutes pronouns in the agent description without regard for grammar. In this example, the generated description is

Agent to give interesting facts. I are a helpful agent who can provide interesting facts.

It should be I am a helpful agent...

Code to Reproduce with version 1.8.0

from google.adk import Agent
from google.adk.a2a.utils.agent_to_a2a import to_a2a
from google.adk.tools import google_search


root_agent = Agent(
    name='facts_agent',
    model='gemini-2.5-flash-lite',
    description=('Agent to give interesting facts.'),
    instruction=('You are a helpful agent who can provide interesting facts.'),
    tools=[google_search],
)

a2a_app = to_a2a(root_agent, port=8001)