feat: add SSH key passphrase field and file picker for key path

- Add ssh_key_passphrase field to ConnectionConfig model with full keyring lifecycle
- Pass passphrase to russh load_secret_key for encrypted SSH keys
- Add native file picker (FolderOpen icon) next to SSH key path input
- Add password-type input for key passphrase in connection dialog
- Make connection dialog form scrollable for short windows
- Fix alignment of key path input and browse button
- Add i18n keys (en + zh-CN)

src-tauri/src/db/ssh_tunnel.rs

@@ -28,6 +28,7 @@ async fn connect_and_authenticate(
     ssh_user: &str,
     ssh_password: &str,
     ssh_key_path: &str,
+    ssh_key_passphrase: &str,
 ) -> Result<Handle<SshClient>, String> {
     let config = Arc::new(Config {
         nodelay: true,
@@ -39,7 +40,8 @@ async fn connect_and_authenticate(
         .map_err(|e| format!("SSH connection failed: {e}"))?;
 
     if !ssh_key_path.is_empty() {
-        let key_pair = load_secret_key(ssh_key_path, None)
+        let passphrase = if ssh_key_passphrase.is_empty() { None } else { Some(ssh_key_passphrase) };
+        let key_pair = load_secret_key(ssh_key_path, passphrase)
             .map_err(|e| format!("Failed to load SSH key: {e}"))?;
         let auth_res = session
             .authenticate_publickey(
@@ -158,6 +160,7 @@ impl TunnelManager {
         ssh_user: &str,
         ssh_password: &str,
         ssh_key_path: &str,
+        ssh_key_passphrase: &str,
         remote_host: &str,
         remote_port: u16,
         expose_to_lan: bool,
@@ -165,7 +168,7 @@ impl TunnelManager {
         let local_port = portpicker::pick_unused_port().ok_or("No available port")?;
 
         let session =
-            connect_and_authenticate(ssh_host, ssh_port, ssh_user, ssh_password, ssh_key_path)
+            connect_and_authenticate(ssh_host, ssh_port, ssh_user, ssh_password, ssh_key_path, ssh_key_passphrase)
                 .await?;
 
         let bind_addr = if expose_to_lan { "0.0.0.0" } else { "127.0.0.1" };