feat(cli): add helpers module (vault_dir/L8, git_command/H4, iso8601/M11)

Bumps rpassword to 7.x (H7) and adds zeroize/chrono/assert_cmd dev-deps.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

crates/relicario-cli/src/main.rs

@@ -37,6 +37,8 @@
 //! binary small and the build simple. Every mutation (add, edit, rm, device add/revoke)
 //! creates a git commit, preserving an audit log of all vault changes.
 
+mod helpers;
+
 use anyhow::{bail, Context, Result};
 use clap::{Parser, Subcommand};
 use relicario_core::{