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

src/shell/actions/drag_out_win.h

@@ -26,13 +26,10 @@ namespace reasampler {
 // (DROPEFFECT_COPY); the return is advisory — a failed drag surfaces no error.
 bool initiateDragOut(HWND__* panelHwnd, const std::vector<std::string>& absolutePaths);
 
-// Cheap, side-effect-free readiness probe: true iff initiateDragOut would actually be able to
-// START a drag for `absolutePaths` right now. Call this BEFORE tearing down internal drag
-// state (release capture, clear drag fields) — an OS that isn't ready (OLE unavailable, or the
-// path list can't build a CF_HDROP) must not consume the gesture the same way an empty payload
-// would. On Windows this re-runs the same OLE-init + HDROP-build checks initiateDragOut does,
-// freeing the probe HGLOBAL immediately; SWELL exposes no such probe, so macOS/Linux reduces to
-// the non-empty check alone.
+// Side-effect-free readiness probe for initiateDragOut. Call BEFORE tearing down internal drag
+// state — an OS that isn't ready (OLE unavailable, HDROP build failure) must not consume the
+// gesture like an empty payload would. Windows re-runs the OLE-init + HDROP checks and frees the
+// probe HGLOBAL immediately; SWELL exposes no probe, so macOS/Linux reduces to the non-empty check.
 bool canInitiateDragOut(const std::vector<std::string>& absolutePaths);
 
 } // namespace reasampler