chore: remove legacy dependency files

[Pigbibi]

Summary

• remove root requirements.txt and constraints.txt as legacy dependency entry points
• install the local project with uv sync --frozen instead of --no-install-project
• keep CI, Docker, and Cloud Run env sync on pyproject.toml + uv.lock
• bump package metadata to 0.3.0

Validation

• uv sync --frozen --extra test
• uv build
• uv pip check
• uv run --no-sync python scripts/check_qpk_pin_consistency.py
• targeted dependency workflow tests
• git diff --check
• local docker build