Add the Create Channel dialog

The official client creates and edits channels with one dialog, so
ChannelEditDialog becomes ChannelDialog with two entry points. Creating
starts from caller-chosen defaults instead of a channelinfo and sends a
channelcreate carrying only what deviates from a plain new channel —
TeamSpeak checks a create permission per property that is present.

The server row now has a context menu with "Create Channel" and "Create
Spacer" (pre-filled with the lowest free [spacerN], since channel names
must be unique), and a channel's menu offers "Create Channel" and
"Create Sub-Channel", both starting out temporary.

Verified against the test server: a temporary channel is created, and a
permanent one a guest may not create reports the server's refusal.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

ts3-client/swing/src/main/java/com/ts3client/ui/ChannelAdvancedPanel.java

@@ -23,7 +23,7 @@ import java.awt.Insets;
  * The channel editor's "Advanced" tab: the phonetic name, the delete delay of a temporary
  * channel, voice encryption, and the two client limits.
  */
-final class ChannelAdvancedPanel extends JPanel implements ChannelEditDialog.Tab {
+final class ChannelAdvancedPanel extends JPanel implements ChannelDialog.Tab {
 
     /** TeamSpeak's ceiling for {@code channel_delete_delay}, in seconds. */
     private static final int MAX_DELETE_DELAY = 604800;