Add OAth flow for Gmail and update tables and UI

Models/Correspondence.cs

@@ -13,6 +13,7 @@ namespace JobTrackerApi.Models
     public string From { get; set; } = ""; // "Me" or "Company"
     public string? Subject { get; set; }
     public string? Channel { get; set; } // e.g. Email, Call, Note
+    public string? ExternalMessageId { get; set; }
     public string Content { get; set; } = "";
     public DateTime Date { get; set; } = DateTime.Now;
 }

Models/GmailConnection.cs

@@ -0,0 +1,14 @@
+namespace JobTrackerApi.Models;
+
+public sealed class GmailConnection
+{
+    public int Id { get; set; }
+    public string OwnerUserId { get; set; } = "";
+    public string GmailAddress { get; set; } = "";
+    public string EncryptedRefreshToken { get; set; } = "";
+    public string? EncryptedAccessToken { get; set; }
+    public DateTimeOffset? AccessTokenExpiresAt { get; set; }
+    public string Scope { get; set; } = "";
+    public DateTimeOffset ConnectedAt { get; set; } = DateTimeOffset.UtcNow;
+    public DateTimeOffset? LastSyncedAt { get; set; }
+}