fix: insert onto selected track(s) at edit cursor, not a new track

Wire both insert actions to CurrentTrack (InsertMedia base 0). Per selected
track: SetOnlyTrackSelected, reset cursor to snapshot, InsertMedia; then restore
original selection + cursor. No-op when no track selected. Corrected stale
extraflags / new-track / preservePitch comments.

src/insert.h

@@ -27,7 +27,7 @@ class ReaSamplerSession;
 // tempo-conform choice) so the two action variants (native-length vs
 // conform-to-tempo) differ only by this struct — no divergent code paths.
 struct InsertRequest {
-    InsertOptions options;  // defaults: new track, no conform, native length
+    InsertOptions options;  // defaults: current track, no conform, native length
 };
 
 // The outcome of an insert action, for the caller to log to the console.
@@ -44,16 +44,19 @@ struct InsertResult {
     int skipped  = 0;   // selected-but-unresolvable/unreadable samples skipped
 };
 
-// Runs the insert: reads bank_panel's selection, resolves each sample against the
-// current project dir, and inserts them AT THE EDIT CURSOR in bank order, advancing
-// the cursor so multiple samples lay end-to-end. The whole placement is wrapped in
-// a single Undo_BeginBlock2 / Undo_EndBlock2 so one undo removes the entire insert.
-// `session` supplies the live bank the selected ids resolve against.
+// Runs the insert: reads the bank panel's single focused sample and the user's
+// currently-selected track set, then inserts the sample onto EACH selected track
+// at the SAME edit-cursor position. Snapshot/restore ensures the user's track
+// selection and cursor position are unchanged after the action. The whole operation
+// is wrapped in a single Undo_BeginBlock2 / Undo_EndBlock2.
 //
-// Multi-select behavior: each selected sample is inserted sequentially at the
-// then-current edit cursor; InsertMedia advances the cursor to the end of the
-// inserted media, so N samples lay contiguously left-to-right. Single-select is the
-// N==1 case of the same path.
+// No-op cases (with console messages):
+//   - No track selected: prints "select a track first."
+//   - No sample selected in the panel: NoSelection status.
+//   - Unsaved project (no resolvable bank dir): NoProject status.
+//   - Sample id not in bank / file missing: NothingResolved status.
+//
+// `session` supplies the live bank the selected id resolves against.
 InsertResult runInsert(ReaSamplerSession* session, const InsertRequest& request);
 
 } // namespace reasampler