[codex] use uv dependency lock

[Pigbibi]

Summary

• Move CI, Docker, and Cloud Run env-sync dependency installation to pyproject.toml + a real uv.lock.
• Keep legacy requirements.txt / constraints.txt for compatibility during the staged migration.
• Use --no-install-project because package-layout migration is intentionally out of scope for this dependency-management PR.
• Add uv workflow regression coverage and tighten .dockerignore so local venv/build artifacts are not copied into Docker context.

Validation

• uv sync --frozen --extra test --no-install-project
• uv run --no-sync python scripts/check_qpk_pin_consistency.py
• uv run --no-sync python -m pytest -q tests/test_uv_dependency_workflow.py tests/test_dependency_pin_guard.py
• bash tests/test_sync_cloud_run_env_workflow.sh
• uv run --no-sync ruff check --exclude external .
• actionlint .github/workflows/ci.yml .github/workflows/sync-cloud-run-env.yml
• git diff --check
• docker build -t longbridgeplatform-uv-sync:local .

Known caveat

• The existing CI unit-test step remains non-blocking via || true; this PR does not change that broader test policy.