Adiciona backup geral no painel master

src/main/webapp/master/backup.html

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+<!doctype html><html lang="pt-BR"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1"><title>Backup</title><link rel="stylesheet" href="/css/app.css"><script src="/js/auth.js"></script><script src="/js/util.js"></script><script src="/js/api.js"></script><script src="/js/layout.js"></script></head><body><main><div class="topbar"><h1>Backup</h1></div><section class="panel"><h2>Backup geral</h2><p class="muted">Baixe um arquivo ZIP com o banco Master e os bancos de todos os clientes cadastrados.</p><button id="backup-btn" class="btn" type="button">Gerar e baixar backup</button><div id="backup-status" class="panel-block muted"></div></section></main><script>Layout.mount('master','backup');</script><script src="/master/backup.js"></script></body></html>

src/main/webapp/master/backup.js

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+const btn=document.querySelector('#backup-btn'),statusEl=document.querySelector('#backup-status');
+btn.onclick=async()=>{
+  if(!confirm('Gerar backup geral do sistema e de todos os clientes?'))return;
+  btn.disabled=true;
+  statusEl.textContent='Gerando backup...';
+  try{
+    const headers={};
+    const token=Auth.token();
+    if(token)headers.Authorization=`Bearer ${token}`;
+    const res=await fetch('/api/master/backup',{headers});
+    if(res.status===401){Auth.logout();return}
+    if(!res.ok){
+      const data=await res.json().catch(()=>({}));
+      throw new Error(data.mensagem||data.erro||`Erro HTTP ${res.status}`);
+    }
+    const blob=await res.blob();
+    const cd=res.headers.get('Content-Disposition')||'';
+    const match=cd.match(/filename="?([^"]+)"?/);
+    const filename=match?match[1]:'seconectai-backup.zip';
+    const url=URL.createObjectURL(blob);
+    const a=document.createElement('a');
+    a.href=url;
+    a.download=filename;
+    document.body.appendChild(a);
+    a.click();
+    a.remove();
+    URL.revokeObjectURL(url);
+    statusEl.textContent='Backup baixado com sucesso.';
+    Util.toast('Backup baixado');
+  }catch(e){
+    statusEl.textContent='';
+    Util.toast(e.message,true);
+  }finally{
+    btn.disabled=false;
+  }
+};