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/panel/panel_bank_ops.cpp

@@ -251,7 +251,7 @@ enum : unsigned int {
 }  // namespace
 
 // Shows the right-click context menu for a named-bank TAB: activate / rename / delete
-// / evacuate that bank, plus a create entry. Drives the id-keyed ops.
+// / evacuate / export that bank, plus a create entry. Drives the id-keyed ops.
 void showTabMenu(int screenX, int screenY, const std::string& bankId) {
     if (!book()) return;
     const Bank* bk = book()->bank(bankId);