Fix drag-drop review findings: unify teardown, gate FX-add on outside-panel, trim comments

src/shell/panel/panel_drag.cpp

@@ -327,13 +327,7 @@ void onMouseMove(int x, int y) {
             // DoDragDrop runs its own modal loop and takes over mouse capture, so the internal
             // drag must be fully wound down first.
             if (GetCapture() == g_panel.hwnd) ReleaseCapture();
-            g_panel.dragArmed = false;
-            g_panel.dragging = false;
-            g_panel.dropKind = DropKind::None;
-            g_panel.dropBankId.clear();
-            g_panel.cardGesture = CardGesture::None;
-            g_panel.dragTargetSlot = -1;
-            g_panel.dragPrimaryId.clear();
+            resetDragState();
             invalidatePanel();
 
             initiateDragOut(g_panel.hwnd, paths);  // COPY-ONLY; blocking on Windows
@@ -424,7 +418,7 @@ void onLBtnUp(int x, int y) {
             const FxDropTarget fx = resolveFxDropTarget(sp.x, sp.y);
             if (fx.valid()) dropTrack = fx.track;
         }
-        if (dropTrack && singleCapture) {
+        if (!inside && dropTrack && singleCapture) {
             const std::string sampleId = g_panel.dragSampleIds.front();
             performInstrumentDrop(dropTrack, buildInstrumentDropPreset(sampleId));
             // Read-only over the bank + arrange: the only mutations are the new FX instance +
@@ -440,8 +434,6 @@ void onLBtnUp(int x, int y) {
             } else if (g == CardGesture::Replace) {
                 // Replace targets the OCCUPANT of the target slot with the single grabbed card.
                 const bool isBanks = g_panel.dragSourceRegion == Region::Banks;
-                RECT cr{};
-                GetClientRect(g_panel.hwnd, &cr);
                 const int w = cr.right - cr.left, h = cr.bottom - cr.top;
                 const RECT region = isBanks ? banksRegionRect(w, h) : poolRegionRect(w, h);
                 const RegionDisplay disp = regionDisplay(region, isBanks, g_panel.dragSourceRegion);