feat(S9/S8): bank-generation change-detection + instrument-side assignment reader

Extension stamps a monotonic bank_generation counter, bumped at content
mutations; the VST3 instrument polls it off-thread on an editor timer and
consumes assignment requests, refreshing playback hands-free.

src/bank_panel.cpp

@@ -2059,7 +2059,10 @@ void doDeleteBank(const std::string& bankId) {
         // r == 6 (Yes) falls through to a plain delete (drops members).
     }
     if (!book()->deleteBank(bankId)) return;
-    persistBankOp("ReaSampler: delete bank");
+    // S9: bump when the bank held samples (either the Yes-drop path or the No-evacuate-then-
+    // delete path moved/dropped members) — both change what a live instance could play. An
+    // empty-bank delete is purely organizational, no bump.
+    persistBankOp("ReaSampler: delete bank", /*bumpGeneration=*/members > 0);
     // shownBankId is reconciled by the next fingerprint pass. If no named banks remain,
     // nudge focus to the pool so the selection has a valid home.
     if (namedBanks().empty()) g_panel.focusedRegion = Region::Pool;
@@ -2071,7 +2074,7 @@ void doEvacuateBank(const std::string& bankId) {
     const Bank* bk = book()->bank(bankId);
     if (!bk || bk->isPool()) return;
     if (!book()->evacuate(bankId)) return;
-    persistBankOp("ReaSampler: evacuate bank");
+    persistBankOp("ReaSampler: evacuate bank", /*bumpGeneration=*/true);  // S9: membership changed
     invalidatePanel();
 }
 
@@ -2115,7 +2118,7 @@ void transferSamples(const std::vector<std::string>& sampleIds,
     if (!mutated) return;  // nothing changed — no persist, no undo point
 
     const char* label = copy ? "ReaSampler: copy sample(s)" : "ReaSampler: move sample(s)";
-    persistBankOp(label);
+    persistBankOp(label, /*bumpGeneration=*/true);  // S9: bank membership changed
     // The selection indexed into the source; after a move those indices are stale, so
     // clear it (the fingerprint pass will also clear, but do it now for immediacy).
     g_panel.selection = Selection{};
@@ -2140,7 +2143,7 @@ void removeSamples(const std::vector<std::string>& sampleIds,
             ++removed;
     if (removed == 0) return;  // nothing changed — no persist, no undo point
 
-    persistBankOp("ReaSampler: remove sample(s)");
+    persistBankOp("ReaSampler: remove sample(s)", /*bumpGeneration=*/true);  // S9: sample dropped
     // The selection indexed into the source; after a remove those indices are stale, so
     // clear it (the fingerprint pass will also clear, but do it now for immediacy).
     g_panel.selection = Selection{};