fix: preserva email no login quando senha incorreta

- Passa email como parametro na URL de erro
- Preenche campo automaticamente ao recarregar
- Foca no campo senha quando email ja preenchido

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

public/login.html

@@ -168,7 +168,13 @@
       el.textContent = 'E-mail ou senha incorretos.';
       el.style.display = 'block';
     }
-    document.getElementById('email').focus();
+    const emailParam = params.get('email');
+    if (emailParam) {
+      document.getElementById('email').value = emailParam;
+      document.getElementById('senha').focus();
+    } else {
+      document.getElementById('email').focus();
+    }
   </script>
 </body>
 </html>

server.js

@@ -55,9 +55,10 @@ app.get('/login', (req, res) => {
 // Unified Login POST - detects role and redirects accordingly
 app.post('/login', async (req, res) => {
   const { email, senha } = req.body;
+  const emailParam = encodeURIComponent(email || '');
   try {
     const user = await authenticate(email, senha);
-    if (!user) return res.redirect('/login?error=1');
+    if (!user) return res.redirect(`/login?error=1&email=${emailParam}`);
 
     // Unified session
     req.session.user = {
@@ -76,7 +77,7 @@ app.post('/login', async (req, res) => {
     }
   } catch (err) {
     console.error('Login error:', err);
-    res.redirect('/login?error=1');
+    res.redirect(`/login?error=1&email=${emailParam}`);
   }
 });