Add Missing Includes Across src/slic3r/GUI

Every GUI source and header now directly includes the headers declaring what it uses, rather than relying on the precompiled header or transitive includes. Generated with clang-tidy misc-include-cleaner, plus one hand edit making CalibrationPanel.hpp self-contained.

src/slic3r/GUI/DockPanel.cpp

@@ -4,10 +4,13 @@
 #include "Plater.hpp"
 #include "Widgets/WebHosting.hpp"
 
+#include <string>
+#include "slic3r/GUI/WebPanel.hpp"
 #include <wx/weakref.h>
 
 #include <algorithm>
 #include <utility>
+#include <wx/webview.h>
 
 namespace Slic3r { namespace GUI {