fix: test_version uses hardcoded version string, breaks release-plz CI

[randomm]

Problem

The test_version integration test in tests/integration.rs:39-44 asserts against a hardcoded version 0.1.0. When release-plz bumps the version (e.g. to 0.1.1 in PR #24), this test fails because the binary outputs the new version but the test still expects the old one. This blocks every future release-plz PR.

CI run: https://github.com/randomm/oo/actions/runs/22620308955/job/65543396253

Fix

Replace the hardcoded version with env!(CARGO_PKG_VERSION) so the test always matches the actual compiled version from Cargo.toml.

Quality Gates (Non-Negotiable)

• All tests pass locally (cargo test)
• cargo clippy -- -D warnings clean
• cargo fmt --check clean
• Coverage stable (no regression below 70%)