feat: Add Enter key support for admin password input

UX improvement:
- Password input now accepts Enter key to submit
- Added onkeypress=handleAdminKeyPress(event) to input field
- New function handleAdminKeyPress(e) checks for Enter key
- Enter key triggers submitAdminLogin()

Implementation:
- Modified showAdminLoginModal() to add onkeypress handler
- Added handleAdminKeyPress(e) function
- Supports both e.key==='Enter' and e.keyCode===13 (cross-browser)

User workflow:
1. Open Settings → Password modal appears
2. Type password: admin123
3. Press Enter → Login submits (no need to click button)
4. Or click Login button → Both methods work

Files changed: src/page.html (+8 lines)

UX: Faster login, keyboard-friendly interface

src/page.html

@@ -197,7 +197,7 @@ function showAdminLoginModal(){
         m.id='mb-admin-modal';
         m.innerHTML='<button class=mb-admin-close onclick=this.parentElement.classList.remove("active")>✕</button>'+
         '<div class=mb-admin-title>Admin Authentication Required</div>'+
-        '<input class=mb-admin-input type=password id=admin-password placeholder="Enter admin password">'+
+        '<input class=mb-admin-input type=password id=admin-password placeholder="Enter admin password" onkeypress=handleAdminKeyPress(event)>'+
         '<button class=mb-admin-btn onclick=submitAdminLogin()>Login</button>'+
         '<div class=mb-admin-error id=admin-error></div>';
         document.body.appendChild(m);
@@ -209,6 +209,12 @@ function showAdminLoginModal(){
     document.getElementById('admin-password').focus();
 }
 
+function handleAdminKeyPress(e){
+    if(e.key==='Enter'||e.keyCode===13){
+        submitAdminLogin();
+    }
+}
+
 function submitAdminLogin(){
     var pwd=document.getElementById('admin-password').value;