feat(email): add delivery adapters

Gmail and Graph request explicit send consent and classify provider rejection separately from uncertain transport failure. IMAP remains read-only; no send API is exposed.

JobTrackerApi/Services/EmailProviders/IEmailProvider.cs

@@ -23,9 +23,21 @@ namespace JobTrackerApi.Services.EmailProviders
 
         /// <summary>Full message content (body + attachments metadata).</summary>
         Task<EmailMessageDetail> GetMessageAsync(string ownerUserId, string messageId, CancellationToken cancellationToken);
+
+        Task<EmailDeliveryResult> SendAsync(string ownerUserId, EmailDeliveryRequest request, CancellationToken cancellationToken);
     }
 
-    public sealed record EmailConnectionInfo(string ProviderKey, string Address);
+    public sealed record EmailConnectionInfo(string ProviderKey, string Address, bool CanSend = false);
+
+    public sealed record EmailDeliveryRequest(string To, string Subject, string BodyText, string? ThreadId = null);
+    public sealed record EmailDeliveryResult(string? ExternalMessageId, string? ExternalThreadId);
+
+    public sealed class EmailProviderDeliveryException(string category, bool uncertain, string message, Exception? innerException = null)
+        : Exception(message, innerException)
+    {
+        public string Category { get; } = category;
+        public bool Uncertain { get; } = uncertain;
+    }
 
     public sealed record EmailMessageSummary(string Id, string ThreadId, string Subject, string From, string To, DateTimeOffset? Date, string Snippet);