Notify matching users when a new shift/job is posted (in-app notifications)

- Notification entity + NotificationService: on publish, notify users whose saved prefs match the listing (role/city/+shift type); users with no preference aren't spammed
- Wired into PostShift, PostJob, and Admin Review publish
- 🔔 bell with unread count in the header (@inject) + /Me/Notifications page (mark-all-read on open)
- Reliable in-app delivery (works in Iran without FCM); Web Push can ride the same records later
- Verified: employee pref → employer posts matching shift → employee bell=۱ + 'شیفت جدید: پزشک عمومی'

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

src/JobsMedical.Web/Models/Notification.cs

@@ -0,0 +1,20 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace JobsMedical.Web.Models;
+
+/// <summary>An in-app notification for a user (e.g. a new shift/job matching their preferences).
+/// Reliable in Iran regardless of Web Push/FCM; a push can ride on top of the same records.</summary>
+public class Notification
+{
+    public long Id { get; set; }
+
+    public int UserId { get; set; }
+    public User User { get; set; } = null!;
+
+    [Required, MaxLength(200)] public string Title { get; set; } = "";
+    [MaxLength(500)] public string? Body { get; set; }
+    [MaxLength(300)] public string? Url { get; set; }
+
+    public bool IsRead { get; set; }
+    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+}