fix(agenda): fix $.map crash and getPacientes type mismatch; restore preloader

AgendaView:
- Fix agendamentos?.filter(...).map(...) crash: optional chain didn't guard .map when agendamentos is null on initial render
- Fix getPacientes fetcher to extract .data array — API now returns {data, total} not Paciente[], causing searchResults.map crash

LoginView:
- Restore 3s preloader splash screen with {APP_VERSION} instead of hardcoded version string

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/views/LoginView.tsx

@@ -1,5 +1,5 @@
-import React, { useState } from 'react';
-import { Database, Lock, User, ArrowRight, ShieldCheck } from 'lucide-react';
+import React, { useState, useEffect } from 'react';
+import { Database, Lock, User, ArrowRight, ShieldCheck, Loader2 } from 'lucide-react';
 import { HybridBackend } from '../services/backend.ts';
 import { APP_VERSION } from '../constants.ts';
 
@@ -12,6 +12,22 @@ export const LoginView: React.FC<LoginViewProps> = ({ onLoginSuccess }) => {
     const [password, setPassword] = useState('');
     const [loading, setLoading] = useState(false);
     const [error, setError] = useState('');
+    const [isInitializing, setIsInitializing] = useState(true);
+
+    useEffect(() => {
+        const timer = setTimeout(() => setIsInitializing(false), 3000);
+        return () => clearTimeout(timer);
+    }, []);
+
+    if (isInitializing) {
+        return (
+            <div className="min-h-screen bg-gray-50 flex flex-col items-center justify-center p-4">
+                <Loader2 className="animate-spin text-blue-600 mb-4" size={48} />
+                <h2 className="text-gray-500 font-bold uppercase tracking-widest text-sm">Inicializando Sistema...</h2>
+                <span className="text-gray-400 text-xs mt-2 font-mono font-bold bg-gray-200 px-2 py-1 rounded">{APP_VERSION}</span>
+            </div>
+        );
+    }
 
     const handleSubmit = async (e: React.FormEvent) => {
         e.preventDefault();