fix: S12 R2 — marker-drag sets selectedZone_, ADSR rate-resolve, gateAdsr doc

Marker drag now sets selectedZone_ so single-capture controls stay reachable. Lifted/default ADSR rescales nominal 44100-Hz frame counts by sampleRate/44100 via adsrNeedsRateResolve; v4-authored zones skip rescale. gateAdsr documented vestigial.

src/vst/reasampler_editor.h

@@ -172,8 +172,9 @@ private:
 
     // Write `m` as a loop/start override upsert into map_ for selectedId_ (find-or-append).
     // Does NOT call commitAndReload — callers decide whether this is a live-drag update or a
-    // final commit. selectedId_ must be non-empty before calling.
-    void upsertPickedOverride(const SetupMarkers& m);
+    // final commit. selectedId_ must be non-empty before calling. Returns the zone index
+    // (0-based) that was updated or appended, so callers can set selectedZone_.
+    int upsertPickedOverride(const SetupMarkers& m);
 
     // --- S12/S15/S16 parameter surface (Zones panel, keyed to selectedZone_) ------
     //