fix: bank indexing off-by-one — subtract 1 when sending bank to API

Client stores bank as b.number+1 (1-based) but the API expects
0-based bank numbers. Caused preset activation to load the wrong
empty preset (bank 1 instead of bank 0), so blocks never appeared.

src/App.jsx

@@ -649,7 +649,7 @@ export default function App(){
     const p=presets.find(pr=>pr.num===num);
     if(!p)return;
     setCurrentPreset(num);
-    await handleLoadPreset(p.bank||1,num-1);
+    await handleLoadPreset((p.bank||1)-1,num-1);
   },[presets,handleLoadPreset]);
 
   // ── Blocks ──
@@ -702,14 +702,14 @@ export default function App(){
     const next=Math.min(currentBank+1,8);
     setCurrentBank(next);
     const bp=presets.filter(p=>p.bank===next);
-    if(bp.length>0)handleLoadPreset(bp[0].bank,bp[0].num-1);
+    if(bp.length>0)handleLoadPreset(bp[0].bank-1,bp[0].num-1);
   },[currentBank,presets,handleLoadPreset]);
 
   const handleBankDown=useCallback(()=>{
     const next=Math.max(currentBank-1,1);
     setCurrentBank(next);
     const bp=presets.filter(p=>p.bank===next);
-    if(bp.length>0)handleLoadPreset(bp[0].bank,bp[0].num-1);
+    if(bp.length>0)handleLoadPreset(bp[0].bank-1,bp[0].num-1);
   },[currentBank,presets,handleLoadPreset]);
 
   const handleGlobalBypass=useCallback(()=>{