🔒 Remove hardcoded passwords, add first-run setup wizard

backend/templates/login.html

@@ -5,7 +5,10 @@
     <div class="col-md-5 col-lg-4">
         <div class="card shadow">
             <div class="card-body p-4">
-                <h3 class="card-title text-center mb-4">🔐 Sign In</h3>
+                <div class="text-center mb-4">
+                    <span style="font-size: 2.5rem;">🏔️</span>
+                    <h4 class="mt-2">Vela Platform</h4>
+                </div>
                 <form id="loginForm">
                     <div class="mb-3">
                         <label for="username" class="form-label">Username</label>
@@ -20,9 +23,6 @@
                     <div id="loginError" class="alert alert-danger d-none py-2"></div>
                     <button type="submit" class="btn btn-primary w-100">Sign In</button>
                 </form>
-                <p class="text-muted text-center mt-3 mb-0" style="font-size: 0.85rem;">
-                    Demo: admin / admin123 &nbsp;|&nbsp; viewer / viewer123
-                </p>
             </div>
         </div>
     </div>