fix(mail): apply search limit and propagate body read error

- Cap search results to limit (keep most-recent UIDs)
- Propagate io.ReadAll errors from body reads in fetchByUIDSet

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/mail/imap.go

@@ -83,7 +83,10 @@ func (c *Client) fetchByUIDSet(folder string, set *imap.SeqSet, full bool) ([]Me
 		if r == nil {
 			continue
 		}
-		raw, _ := io.ReadAll(r)
+		raw, err := io.ReadAll(r)
+		if err != nil {
+			return nil, fmt.Errorf("uid %d: read body: %w", m.Uid, err)
+		}
 		parsed, err := ParseMessage(m.Uid, raw)
 		if err != nil {
 			return nil, err
@@ -187,6 +190,9 @@ func (c *Client) Search(folder string, sc SearchCriteria, limit int) ([]Header,
 	if len(uids) == 0 {
 		return nil, nil
 	}
+	if limit > 0 && len(uids) > limit {
+		uids = uids[len(uids)-limit:] // keep highest (most recent) UIDs
+	}
 	return c.FetchHeaders(folder, uids)
 }