cli: avoid data-dir initialization for version; create db parent dirs; redact generated passwords in CLI output

- Prevent 'nx9-wg version' from creating data directories by avoiding database initialization.
- Create parent directories when an explicit --database path is provided.
- Redact printed generated administrator passwords; announce file path or redact instead.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

crates/nx9-wg-core/src/error.rs

@@ -0,0 +1,37 @@
+//! Error types for nx9-wg.
+
+#[derive(Debug, thiserror::Error)]
+pub enum Nx9Error {
+    /// Validation error
+    #[error("Validation error: {0}")]
+    Validation(String),
+    /// Database error
+    #[error("Database error: {0}")]
+    Database(String),
+    /// WireGuard error
+    #[error("WireGuard error: {0}")]
+    WireGuard(String),
+    /// Network error
+    #[error("Network error: {0}")]
+    Network(String),
+    /// Authentication error
+    #[error("Auth error: {0}")]
+    Auth(String),
+    /// Cryptography error
+    #[error("Crypto error: {0}")]
+    Crypto(String),
+    /// Backup error
+    #[error("Backup error: {0}")]
+    Backup(String),
+    /// Configuration error
+    #[error("Config error: {0}")]
+    Config(String),
+    /// I/O error
+    #[error("I/O error: {0}")]
+    Io(#[from] std::io::Error),
+    /// Internal error
+    #[error("Internal error: {0}")]
+    Internal(String),
+}
+
+pub type Result<T> = std::result::Result<T, Nx9Error>;