[UI] Responsive hamburger nav for mobile

- _Layout: wrap nav + actions in .nav-collapse; add CSS-only burger
  (checkbox toggle) + always-visible mobile bell next to it
- site.css: desktop layout unchanged; <=860px collapses nav into a
  full-width dropdown (column links, stacked actions), animated open
- Login (ورود) + logout render as full-width buttons in the menu
  instead of overflowing the header row

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/JobsMedical.Web/Pages/Shared/_Layout.cshtml

@@ -36,36 +36,50 @@
                 <span class="brand-mark">ه</span>
                 <span class="brand-text">همکادر</span>
             </a>
-            <nav class="main-nav">
-                <a asp-page="/Index">خانه</a>
-                <a asp-page="/Shifts/Index">شیفت‌ها</a>
-                <a asp-page="/Jobs/Index">استخدام</a>
-                <a asp-page="/Calendar/Index">تقویم هفتگی</a>
-                <a asp-page="/Download">دریافت اپ</a>
-                <a asp-page="/Facilities/Index">مراکز درمانی</a>
-                <a asp-page="/Preferences/Index">علاقه‌مندی‌ها</a>
-            </nav>
-            <div class="header-actions">
-                @if (User.Identity?.IsAuthenticated == true)
-                {
-                    @if (User.IsInRole("Admin"))
+
+            @* Always-visible bell on mobile (next to the burger) so notifications stay one tap away *@
+            @if (User.Identity?.IsAuthenticated == true)
+            {
+                <a class="bell-mobile" asp-page="/Me/Notifications" title="اعلان‌ها">🔔@if (unreadCount > 0) {<span class="bell-badge">@JalaliDate.ToPersianDigits(unreadCount > 99 ? "99+" : unreadCount.ToString())</span>}</a>
+            }
+
+            <input type="checkbox" id="nav-toggle" class="nav-toggle" hidden />
+            <label for="nav-toggle" class="nav-burger" aria-label="باز/بستن منو">
+                <span></span><span></span><span></span>
+            </label>
+
+            <div class="nav-collapse">
+                <nav class="main-nav">
+                    <a asp-page="/Index">خانه</a>
+                    <a asp-page="/Shifts/Index">شیفت‌ها</a>
+                    <a asp-page="/Jobs/Index">استخدام</a>
+                    <a asp-page="/Calendar/Index">تقویم هفتگی</a>
+                    <a asp-page="/Download">دریافت اپ</a>
+                    <a asp-page="/Facilities/Index">مراکز درمانی</a>
+                    <a asp-page="/Preferences/Index">علاقه‌مندی‌ها</a>
+                </nav>
+                <div class="header-actions">
+                    @if (User.Identity?.IsAuthenticated == true)
                     {
-                        <a asp-page="/Admin/Overview" style="margin-inline-end:14px; font-weight:600;">پنل مدیریت</a>
+                        @if (User.IsInRole("Admin"))
+                        {
+                            <a class="nav-action" asp-page="/Admin/Overview">پنل مدیریت</a>
+                        }
+                        @if (User.IsInRole("FacilityAdmin"))
+                        {
+                            <a class="nav-action" asp-page="/Employer/Index">پنل کارفرما</a>
+                        }
+                        <a class="nav-action bell-inline" asp-page="/Me/Notifications" title="اعلان‌ها">🔔 اعلان‌ها@if (unreadCount > 0) {<span class="bell-badge">@JalaliDate.ToPersianDigits(unreadCount > 99 ? "99+" : unreadCount.ToString())</span>}</a>
+                        <a class="nav-action" asp-page="/Me/Index">پنل کارجو</a>
+                        <form method="post" asp-page="/Account/Logout" style="display:contents;">
+                            <button type="submit" class="btn btn-outline btn-sm">خروج</button>
+                        </form>
                     }
-                    @if (User.IsInRole("FacilityAdmin"))
+                    else
                     {
-                        <a asp-page="/Employer/Index" style="margin-inline-end:14px; font-weight:600;">پنل کارفرما</a>
+                        <a class="btn btn-outline btn-sm" asp-page="/Account/Login">ورود</a>
                     }
-                    <a asp-page="/Me/Notifications" title="اعلان‌ها" style="margin-inline-end:12px; position:relative; font-size:18px;">🔔@if (unreadCount > 0) {<span class="bell-badge">@JalaliDate.ToPersianDigits(unreadCount > 99 ? "99+" : unreadCount.ToString())</span>}</a>
-                    <a asp-page="/Me/Index" style="margin-inline-end:10px; font-weight:600;">پنل کارجو</a>
-                    <form method="post" asp-page="/Account/Logout" style="display:inline;">
-                        <button type="submit" class="btn btn-outline" style="padding:7px 14px;">خروج</button>
-                    </form>
-                }
-                else
-                {
-                    <a class="btn btn-outline" asp-page="/Account/Login">ورود</a>
-                }
+                </div>
             </div>
         </div>
     </header>