import: a .rsbank lands as a new bank, whole or not at all

Four collisions answered explicitly: ids reminted, names never overwritten,
content deduped before the write, bank name auto-suffixed. Degraded ledger
refuses before the picker.

src/shell/actions/package_import_action.h

@@ -0,0 +1,19 @@
+#pragma once
+// package_import_action — the bindable/menu/drop skin over importBankPackage: the
+// ledger gate (which runs BEFORE the picker, so a refusal never costs the user a file
+// choice), the picker itself, and every message the import produces.
+
+#include <string>
+
+namespace reasampler {
+
+class ReaSamplerSession;
+
+// Gate, pick, import, report. The bound action and the panel's bank menu both call this.
+void doImportBankPackage(ReaSamplerSession& session);
+
+// Same, for a .rsbank already named by the user — the panel's file-drop route. The gate
+// still runs first; only the picker is skipped.
+void doImportBankPackageFile(ReaSamplerSession& session, const std::string& packageAbsPath);
+
+}  // namespace reasampler