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.cpp

@@ -306,10 +306,19 @@ void onMouseMove(int x, int y, WPARAM wParam) {
     // A move with the button already up while still dragging means the release was missed (the
     // OS hand-off's own modal loop can eat a WM_LBUTTONUP, and coalescing can lose one too) —
     // treat it as the release now rather than leaving dragging stuck for the next plain click.
+#ifdef _WIN32
     if (g_panel.dragging && !(wParam & MK_LBUTTON)) {
         onLBtnUp(x, y);
         return;
     }
+#else
+    // SWELL never sets wParam on WM_MOUSEMOVE (swell-types.h ~1315), so the button-up test must
+    // read the physical key state instead of the message's own (always-zero) wParam.
+    if (g_panel.dragging && !(GetAsyncKeyState(VK_LBUTTON) & 0x8000)) {
+        onLBtnUp(x, y);
+        return;
+    }
+#endif
 
     // Hover feedback: resolve + repaint-on-change, but NOT during a drag (the drag owns
     // the visual feedback then — a drop-target highlight, not a hover).