Fix SWELL drag guard, channel-fork the VST editor window class, dedupe own-module match

Panel drag no longer misfires on SWELL's always-zero wParam; stable/beta VST editors register distinct window classes against their own module instead of colliding on REAPER's; own-module basename matching moves to a tested pure helper.

src/shell/panel/panel_drag_os.cpp

@@ -1,6 +1,6 @@
-// panel_drag_os.cpp — the OS hand-off / resume seam split out of panel_drag.cpp (the ~600-line
-// file ceiling): the live re-ask the OS drag loop uses to decide whether to keep the drag, the
-// hand-off itself, and resuming the internal drag when the OS loop gives the gesture back.
+// panel_drag_os.cpp — the OS hand-off / resume seam split out of panel_drag.cpp: the live
+// re-ask the OS drag loop uses to decide whether to keep the drag, the hand-off itself, and
+// resuming the internal drag when the OS loop gives the gesture back.
 //
 // Compiled into the reaper_reasampler MODULE. No REAPER API functions are called directly here;
 // REAPER SDK types arrive via panel_state.h.