fix(channels): handle io.ReadAll error in Lark adapter

LarkAdapter.SendMessage ignored the error from io.ReadAll(resp.Body).
When the read failed on a 200 response, the empty body caused
json.Unmarshal to fail, which silently skipped the apiResp.Code check
and returned nil (success). This meant transport failures were treated
as delivered messages. Surface the read error explicitly.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

workspace-server/internal/channels/lark.go

@@ -119,7 +119,10 @@ func (l *LarkAdapter) SendMessage(ctx context.Context, config map[string]interfa
 	}
 	defer func() { _ = resp.Body.Close() }()
 
-	body, _ := io.ReadAll(resp.Body)
+	body, readErr := io.ReadAll(resp.Body)
+	if readErr != nil {
+		return fmt.Errorf("lark: read response body: %w", readErr)
+	}
 	if resp.StatusCode != http.StatusOK {
 		return fmt.Errorf("lark: webhook returned %d: %s", resp.StatusCode, strings.TrimSpace(string(body)))
 	}