v0.3.0 - remove legacy dependency files

v0.3.0

Second-phase dependency-management cleanup release.

• Removes legacy root requirements.txt and constraints.txt dependency entry points.
• Installs the local platform project with uv sync --frozen in CI, Docker, and Cloud Run environment sync.
• Keeps pyproject.toml and uv.lock as the dependency source of truth.
• Adds package discovery for the existing flat-layout modules where needed.
• Keeps the static review gate blocking unexpected file deletions while allowing the intentional removal of legacy dependency manifests.