feat: include Git revision in version output

[rsheyd]

What changed

• include the short Git revision in terminalist --version for builds made from a Git checkout;
• append dirty when tracked working-tree changes were present at build time;
• keep the ordinary package-version output when Git metadata is unavailable, such as packaged builds;
• document how contributors can install and identify a local development build.

Why

Local development builds currently share the package version, which makes it difficult to tell which checkout produced an installed binary. Including the revision makes bug reports and local testing easier without changing release-version semantics.

The build script watches Git's actual HEAD, index, and current branch-ref paths, as well as src and build.rs, so Cargo refreshes the revision and dirty state after commits and working-tree changes. Resolving the paths through Git also supports linked worktrees.

Validation

• cargo fmt --all -- --check
• cargo clippy --all-targets --all-features -- -D warnings
• cargo test
• clean manual check: terminalist 0.5.0 (5c2312a)

[rsheyd]

I’m going to close this in favor of #202.

I originally added Git metadata because CONTRIBUTING.md didn’t provide a convention for identifying development builds. After thinking about it more, documenting -dev.N versions addresses the original need more simply, without adding build-script machinery.