fix: report the real package version in health endpoints

app_version was hardcoded to 1.0.0, and pyproject.toml also said 1.0.0
on the 2.0 release, so /platform/healthz and /platform/readyz reported
the wrong version.

Bump pyproject.toml to 2.0.0 and relock (only OEG's own uv.lock entry
changes). app_version now defaults to the installed package version
from importlib.metadata. If the metadata is missing it falls back to
0.0.0+unknown. APP_VERSION still overrides it.

The Dockerfile's non-editable uv sync keeps the package metadata, so
the image reports 2.0.0.