Replace log.Fatal in IMAP fetch goroutine with error channel

log.Fatal called os.Exit from a goroutine, bypassing deferred cleanup
and crashing the process on any transient fetch error. Errors now
propagate back to the caller via a buffered channel. Also adds a drain
defer so the goroutine can always exit if the consumer returns early.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pkg/email/fetch.go

@@ -64,12 +64,17 @@ func fetchEmails(imapClient *client.Client) ([]Email, error) {
 
 		// Fetch the required message attributes
 		messages := make(chan *imap.Message, 10)
+		fetchErr := make(chan error, 1)
 		section := &imap.BodySectionName{}
 		items := []imap.FetchItem{section.FetchItem(), imap.FetchEnvelope}
 
 		go func() {
-			if err := imapClient.Fetch(seqSet, items, messages); err != nil {
-				log.Fatal("Fetch error: " + err.Error())
+			fetchErr <- imapClient.Fetch(seqSet, items, messages)
+		}()
+
+		// Drain the channel on early return so the goroutine can always exit.
+		defer func() {
+			for range messages {
 			}
 		}()
 
@@ -98,6 +103,10 @@ func fetchEmails(imapClient *client.Client) ([]Email, error) {
 			)
 			result = append(result, *email)
 		}
+
+		if err := <-fetchErr; err != nil {
+			return result, fmt.Errorf("fetch error: %w", err)
+		}
 	}
 
 	return result, nil