feat(banks): bindable multi-bank action family — create/rename/delete/evacuate/activate/move/copy + full-height toggles (B3)

src/bank_book.cpp

@@ -668,6 +668,22 @@ std::optional<BankBook> BankBook::deserialize(const std::string& json) {
     return book;
 }
 
+// ---------------------------------------------------------------------------
+// Active-bank cycle ordering (pure, free function — mirror of nextModeId)
+// ---------------------------------------------------------------------------
+
+std::string nextBankId(const std::vector<std::string>& orderedBankIds,
+                       const std::string& currentBankId) {
+    if (orderedBankIds.empty()) return {};  // nothing to cycle to
+    for (std::size_t i = 0; i < orderedBankIds.size(); ++i) {
+        if (orderedBankIds[i] == currentBankId)
+            return orderedBankIds[(i + 1) % orderedBankIds.size()];  // wrap past the last
+    }
+    // Active id not in the list (stale/unknown) — jump to the first id as a sane
+    // home rather than returning "" (matches nextModeId's fallback).
+    return orderedBankIds.front();
+}
+
 BankBook BankBook::loadFromPersisted(const std::string& banksJson,
                                      const std::string& legacyJson) {
     // Precedence 1: the authoritative `banks` blob. A present-but-malformed blob is