feat(m11): native OS drag-out of bank samples (copy-only)

Pure drag_out (gesture boundary + path-list assembly) + Windows OLE
CF_HDROP / SWELL file-list shell; bank_panel hands off when a dragged
selection leaves the client area. COPY-ONLY mask; internal drag intact.

src/drag_out.cpp

@@ -0,0 +1,48 @@
+// drag_out — pure implementation. See drag_out.h. NO REAPER / SWELL / OS / vendor.
+
+#include "drag_out.h"
+
+#include <unordered_set>
+
+namespace reasampler {
+
+namespace {
+
+// Half-open point-in-rect (matches the panel's other hit-tests: [x, x+w) x [y, y+h)).
+bool insideClient(int px, int py, const PanelClientRect& c) {
+    return px >= c.x && px < c.x + c.width &&
+           py >= c.y && py < c.y + c.height;
+}
+
+} // namespace
+
+DragGesture decideGesture(int px, int py, const PanelClientRect& client,
+                          const DragState& state) {
+    if (!state.dragging || !state.hasArmedSamples) return DragGesture::None;
+    return insideClient(px, py, client) ? DragGesture::Internal : DragGesture::OsDrag;
+}
+
+PathList assemblePathList(const std::vector<ResolvedSample>& resolved) {
+    PathList out;
+    std::unordered_set<std::string> seen;
+    seen.reserve(resolved.size());
+
+    for (const ResolvedSample& s : resolved) {
+        if (s.absolutePath.empty()) {          // shell could not resolve it
+            ++out.skippedUnresolved;
+            continue;
+        }
+        if (!s.fileExists) {                   // stale index entry, file gone
+            ++out.skippedMissing;
+            continue;
+        }
+        if (!seen.insert(s.absolutePath).second) {  // already emitted this path
+            ++out.skippedDuplicate;
+            continue;
+        }
+        out.paths.push_back(s.absolutePath);
+    }
+    return out;
+}
+
+} // namespace reasampler