feat(cli): add --version/-V flag

[JoseVelazcoH]

Summary

tth --version (and -V) now prints the package version, e.g. tth 0.1.1. Previously clap rejected the flag because no version was set on the root command.

Motivation

Every CLI is expected to report its version; there was no way to check which Thoth build you were running short of opening the TUI header.

Changes

• Set version on the root clap #[command(...)], sourced from CARGO_PKG_VERSION.
• Add tests: clap definition debug_assert, and that the exposed version matches the package version.

Test plan

• Unit tests added / updated (662 passing)
• Integration tests added / updated
• Tested locally with cargo test
• Manual: cargo run -- --version prints tth 0.1.1

Review checklist

• Follows commit convention
• No raw SQL without parameterized queries
• No ORM or migration library introduced
• cargo fmt and cargo clippy clean (pre-existing search.rs MSRV warning unrelated)
• Docs updated if public API changed (n/a)

Breaking changes

None.