Add shift-left-click on the sign as a shortcut to destroy the gate

Same permission check as /sg destroy (owner with stargate.destroy, or
stargate.admin). Also breaks the physical sign block via
breakNaturally() so it drops like a normal mined sign instead of just
vanishing, matching what happens when StructureProtectListener reacts
to an actual BlockBreakEvent on the sign.

README.md

@@ -66,6 +66,9 @@ material, unsealed interior, too far from the sign, etc.
 - **Left-click** the sign: dials the shown destination - chevrons light in sequence,
   then the interior becomes the event horizon (`gate.iris-open-material`, default
   water) and travel opens up. It auto-closes after `dialing.open-seconds`.
+- **Shift + left-click** the sign: destroys the gate on the spot (same permission
+  check as `/sg destroy` - owner or `stargate.admin`), breaking the sign as if
+  you'd mined it. Quicker than looking at the sign and typing the command.
 - Travel is **one-way**: only the gate you dialed *from* can send anything anywhere.
   Walking (or wandering, or drifting) into its event horizon teleports whatever
   entered to the destination, arriving just clear of its iris (never inside it) and

stargate-paper/src/main/java/dev/skywalker3200/stargate/paper/listener/SignInteractListener.java

@@ -17,7 +17,7 @@ import org.bukkit.event.player.PlayerInteractEvent;
 
 import java.util.List;
 
-/** Right-click a gate's sign to cycle its destination, left-click to dial it. */
+/** Right-click a gate's sign to cycle its destination, left-click to dial it, shift-left-click to destroy it. */
 public class SignInteractListener implements Listener {
 
     private final StargatePlugin plugin;
@@ -55,9 +55,25 @@ public class SignInteractListener implements Listener {
             SignRenderer.render(rg, gateManager);
             player.playSound(player.getLocation(), Sound.UI_BUTTON_CLICK, 1f, 1f);
         } else if (event.getAction() == Action.LEFT_CLICK_BLOCK) {
+            if (player.isSneaking()) {
+                destroy(rg, block, player);
+            } else {
                 dial(rg, player);
             }
         }
+    }
+
+    private void destroy(RuntimeGate rg, Block signBlock, org.bukkit.entity.Player player) {
+        boolean allowed = player.hasPermission("stargate.admin")
+                || (rg.getGate().getOwner() != null && rg.getGate().getOwner().equals(player.getUniqueId()) && player.hasPermission("stargate.destroy"));
+        if (!allowed) {
+            player.sendMessage(Component.text("You can't destroy this stargate.", NamedTextColor.RED));
+            return;
+        }
+        gateManager.destroyGate(rg);
+        signBlock.breakNaturally();
+        player.sendMessage(Component.text("Destroyed '" + rg.getGate().getName() + "'.", NamedTextColor.YELLOW));
+    }
 
     private void dial(RuntimeGate from, org.bukkit.entity.Player player) {
         if (from.isOpen()) {