Close bank-export review findings: name-cap underflow, double overwrite prompt, test scope

Clamps insertSuffix's underflow, floors uniqueEntryName's validity guard, suppresses
the redundant overwrite confirm via a picker out-param, adds a PayloadBuffer
high-water mark, and corrects stale CLAUDE.md/CMake claims.

src/shell/package/package_pickers.h

@@ -18,7 +18,12 @@ bool pickPackageForImport(std::string& outAbsPath);
 // suggestedPath is a bare file name ("MyBank.rsbank") or a full path — a full one
 // also seeds the dialog's starting directory, which is how a caller keeps the picker
 // off REAPER's process working directory. True with outAbsPath set iff the user chose
-// a destination; the dialog's own overwrite confirm has already run by then.
-bool pickPackageSavePath(const std::string& suggestedPath, std::string& outAbsPath);
+// a destination; the dialog's own overwrite confirm has already run by then, against
+// the path the user actually chose — NOT necessarily outAbsPath, if the `.rsbank`
+// re-append below fires. outAppended, when non-null, is set to whether it fired: the
+// caller's signal that its own overwrite consent may not cover the returned path
+// (see this directory's CLAUDE.md).
+bool pickPackageSavePath(const std::string& suggestedPath, std::string& outAbsPath,
+                         bool* outAppended = nullptr);
 
 }  // namespace reasampler