Merge https://github.com/google/adk-python/pull/2791Fixes#2789
## Summary
Forward `state_delta` from the FastAPI `/run` request to `Runner.run_async(...)`, aligning behavior with the documented
API and the `/run_sse` endpoint.
## Why
The documentation for `/run` explicitly includes:
> `state_delta` (object, optional): A delta of the state to apply before the run.
However, the non‑SSE `/run` handler did not pass this value through, so `Runner.run_async` always received `None`. The
`/run_sse` path already forwarded it correctly.
## Changes
- `src/google/adk/cli/adk_web_server.py`
- Add `state_delta=req.state_delta` to the "/run" handler’s `runner.run_async(...)` call.
- `tests/unittests/cli/test_fast_api.py`
- Add `test_agent_run_passes_state_delta` to test the fix.
COPYBARA_INTEGRATE_REVIEW=https://github.com/google/adk-python/pull/2791 from pguerra-ce:fix-state-delta-missing-in-run 83eec8d28b80757e24ae900285eb59530863adbd
PiperOrigin-RevId: 802703072
