docs: fix stale warp_sdk import in README usage example

[kjankov]

Summary

Fixes a stale import example in the "Using environments and configuration" section of README.md.

The original code block incorrectly referenced a non-existent warp_sdk package and WarpAPI class, and used response.task_id which doesn't match the actual API response shape. This PR updates the example to match all other usage examples in the README.

Changes

Before:

from warp_sdk import WarpAPI

client = WarpAPI()
...
print(response.task_id)

After:

import os
from oz_agent_sdk import OzAPI

client = OzAPI(
    api_key=os.environ.get("WARP_API_KEY"),  # This is the default and can be omitted
)
...
print(response.run_id)

Testing

• ruff check . — all checks passed (no Python code changed, only README.md)
• Change is documentation-only; no runtime behavior affected.

Screenshot

Conversation: http://localhost:8080/conversation/52a1560c-ce51-4ce7-80bc-94edbc640e92
Run: http://localhost:8082/runs/019edc91-9c43-7ba0-b979-89eaac961ffb

This PR was generated with Oz.