fix: route channellist/clientlist/serverinfo through Exec() for reconnect-on-EOF

These callers used unexported ssh.exec() directly, bypassing execSafe()
and its reconnect-on-connection-error logic. When TS6 closed the
persistent SSH session, every HTTP request returned EOF until container
restart. The exported Exec() wraps each call in execSafe which retries
once on isConnectionError with a fresh session.

internal/ts6/channel.go

@@ -31,7 +31,7 @@ type Channel struct {
 // GetChannelList retrieves all channels using ServerQuery (SSH)
 func GetChannelList(cfg *config.Config, ssh *SSHClient) ([]Channel, error) {
 
-	raw, err := ssh.exec("channellist -topic -flags -limits -voice -icon -secondsempty")
+	raw, err := ssh.Exec("channellist -topic -flags -limits -voice -icon -secondsempty")
 	if err != nil {
 		return nil, fmt.Errorf("failed to execute channellist: %w", err)
 	}

internal/ts6/client.go

@@ -45,7 +45,7 @@ func GetClientList(cfg *config.Config, ssh *SSHClient) ([]Client, error) {
 		voiceCmd = "-voice"
 	}
 
-	raw, err := ssh.exec("clientlist -uid -away -groups -times -info -country -icon " + voiceCmd)
+	raw, err := ssh.Exec("clientlist -uid -away -groups -times -info -country -icon " + voiceCmd)
 	if err != nil {
 		return nil, fmt.Errorf("failed to execute clientlist: %w", err)
 	}

internal/ts6/serverinfo.go

@@ -22,7 +22,7 @@ type ServerInfo struct {
 }
 
 func GetServerInfo(cfg *config.Config, c *SSHClient) (*ServerInfo, error) {
-	raw, err := c.exec("serverinfo")
+	raw, err := c.Exec("serverinfo")
 	if err != nil {
 		return nil, fmt.Errorf("failed to execute serverinfo: %w", err)
 	}