Fix broken CLI caused by double-parse bug

[dom-nie]

Summary

PR #408 added an empty Cli struct with Cli::parse() before the real Args::parse() in all three binaries (cli, pbs, signer). Since Cli has no fields or subcommands, clap treats it as a complete parser — --help renders without subcommands and any argument like init is rejected as unexpected. The real Args::parse() is never reached.

This PR:

• Moves the VERSION constant (with "v" prefix) into the shared cb_cli crate
• Removes the empty Cli structs from bin/cli.rs, bin/pbs.rs, and bin/signer.rs
• Adds regression tests for subcommand parsing and version prefix

Fixes #375

Bug reproduction (on main)

$ commit-boost-cli --help
Usage: commit-boost-cli

Options:
  -h, --help     Print help
  -V, --version  Print version

$ commit-boost-cli init --config test.toml
error: unexpected argument 'init' found

After fix

$ commit-boost-cli --version
commit-boost-cli v0.9.3

$ commit-boost-cli --help
Usage: commit-boost-cli <COMMAND>

Commands:
  init  Generate the starting docker-compose file
  help  Print this message or the help of the given subcommand(s)

Test plan

• cargo check passes
• cargo test -p cb-cli passes (2 new tests)
• commit-boost-cli --version shows version with "v" prefix
• commit-boost-cli --help lists init subcommand
• commit-boost-cli init --config <path> works
• commit-boost-pbs --version and commit-boost-signer --version work