🐛 fix(ssh): 修复非 id_rsa 私钥无法浏览选择与读取

- 修正 OpenFileDialog 默认目录，支持无扩展名密钥路径
- macOS 下取消错误文件名过滤，显示隐藏项以选择 ~/.ssh 密钥
- 私钥读/解析失败返回明确错误，示例改为 id_ed25519
- 补充选钥目录解析与私钥读取失败回归测试

Refs #711

internal/ssh/ssh.go

@@ -4,11 +4,13 @@ import (
 	"context"
 	"crypto/sha256"
 	"encoding/hex"
+	"errors"
 	"fmt"
 	"io"
 	"net"
 	"os"
 	"strconv"
+	"strings"
 	"sync"
 	"time"
 
@@ -59,18 +61,22 @@ func connectSSH(config connection.SSHConfig) (*ssh.Client, error) {
 	logger.Infof("开始建立 SSH 连接：地址=%s:%d 用户=%s", config.Host, config.Port, config.User)
 	authMethods := []ssh.AuthMethod{}
 
-	if config.KeyPath != "" {
-		key, err := os.ReadFile(config.KeyPath)
+	if keyPath := strings.TrimSpace(config.KeyPath); keyPath != "" {
+		key, err := os.ReadFile(keyPath)
 		if err != nil {
-			logger.Warnf("读取 SSH 私钥失败：路径=%s，原因：%v", config.KeyPath, err)
-		} else {
-			signer, err := ssh.ParsePrivateKey(key)
-			if err != nil {
-				logger.Warnf("解析 SSH 私钥失败：路径=%s，原因：%v", config.KeyPath, err)
-			} else {
-				authMethods = append(authMethods, ssh.PublicKeys(signer))
-			}
+			logger.Warnf("读取 SSH 私钥失败：路径=%s，原因：%v", keyPath, err)
+			return nil, fmt.Errorf("failed to read SSH private key %s: %w", keyPath, err)
 		}
+		signer, err := ssh.ParsePrivateKey(key)
+		if err != nil {
+			logger.Warnf("解析 SSH 私钥失败：路径=%s，原因：%v", keyPath, err)
+			var passphraseErr *ssh.PassphraseMissingError
+			if errors.As(err, &passphraseErr) {
+				return nil, fmt.Errorf("SSH private key %s is encrypted with a passphrase; passphrase-protected keys are not supported", keyPath)
+			}
+			return nil, fmt.Errorf("failed to parse SSH private key %s: %w", keyPath, err)
+		}
+		authMethods = append(authMethods, ssh.PublicKeys(signer))
 	}
 
 	if config.Password != "" {