Sprint 8: prefer port 16620 for first instance, fall back to any port if taken

NEXT PUSH:
TASK: Fix port 16620 priority regression
FILES CHANGING: Source/Plugin/McpServer.cpp (start() method only)
FILES NOT TOUCHING: all locked files ✅
NEW FILES: none"

Source/Plugin/McpServer.cpp

@@ -70,7 +70,18 @@ void McpServer::start()
     if (running.load()) return;
     serverThread = std::thread([this]() {
         running.store(true);
-        port = server->bind_to_any_port("127.0.0.1");
+
+        // Try preferred port 16620 first (so Claude Code config works without changes)
+        // If taken (another instance already running), fall back to any available port
+        if (server->bind_to_port("127.0.0.1", PluginBridgeConstants::kDefaultMcpPort))
+        {
+            port = PluginBridgeConstants::kDefaultMcpPort;
+        }
+        else
+        {
+            port = server->bind_to_any_port("127.0.0.1");
+        }
+
         server->listen_after_bind();
         running.store(false);
     });