fix(cli): use keyring-core + native platform stores (drop keyring meta-crate)

[BryanFRD]

Closes #163. Supersedes #164 (the cli-feature quick fix, which dragged in clap, rpassword and a SQLite engine).

CI (Rust CLI) has been red on main since the keyring 4.1.0/4.1.1 bumps (#159/#160): keyring 4.1 moved use_native_store behind a cli feature, so keyring::use_native_store no longer resolves with default features.

The keyring maintainers explicitly recommend that real apps link keyring-core + only the platform store crates they need, rather than the keyring meta-crate. This does that:

• Drop the keyring dependency. Keep keyring-core (already used for Entry).
• Add per-target native stores: zbus-secret-service-keyring-store (Linux, crypto-rust), apple-native-keyring-store (macOS, keychain), windows-native-keyring-store (Windows).
• storage.rs sets the default store via keyring_core::set_default_store(<platform>::Store::new_with_configuration(..)) under #[cfg(target_os)]. Behavior is identical to the old use_native_store(true) (Linux → Secret Service via zbus).

No SQLite/clap/rpassword pulled in: the lockfile shrinks (−13 net) instead of the +1443 the cli feature added.

Verified locally on Windows: cargo check, cargo clippy --all-targets -- -D warnings (pedantic on), cargo fmt --check all green. CI covers Linux.