fix(examples): sync stale langgraph-python uv.lock with pyproject (CopilotKit#5271)

## Why

The langgraph-python template's `uv.lock` was stale: it locked
`copilotkit 0.1.87` / `ag-ui-langgraph 0.0.33` while `pyproject.toml`
pins `copilotkit==0.1.93`. Because the lock didn't match, every
scaffold's `uv sync` discarded it and re-resolved fresh against PyPI
latest.

That silent re-resolution is how fresh `copilotkit init` scaffolds
(langgraph-py / a2ui / opengenui) broke today: they picked up
`ag-ui-langgraph 0.0.39`, which imported a then-unpublished
`ag-ui-a2ui-toolkit` symbol and failed at import time (`ImportError:
cannot import name 'run_a2ui_generation_with_recovery'`). The other
python templates (langgraph-fastapi, langgraph-python-threads,
strands-python) survived precisely because their locks are in sync.

## What

Regenerated `uv.lock` with `uv lock` so it matches `pyproject.toml`. It
now locks the fixed pair published by the ag-ui maintainers:
`ag-ui-langgraph 0.0.40` + `ag-ui-a2ui-toolkit 0.0.2` (verified to
import cleanly and load the template graph). With the lock in sync,
scaffolds become deterministic — a future broken upstream release can no
longer break `copilotkit init` until the lock is deliberately updated.

Tracking the upstream release-process issue in OSS-256.

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Author: tylerslaton