review: address Sourcery feedback — neutral language + log error object

Per #2520 review:

1. Drop vendor-specific markers in code comment and log message
   (was '[ZOMBIE-CLEANUP]' and 'RIGARR PATCH'). Comment now describes
   the bug in upstream-friendly terms.

2. Pass the full error object to logger.warn instead of toString(),
   following the existing convention in monitor.service.ts
   ('no.connection' handler) where structured object logging is used
   to preserve diagnostic detail.

No behavior change.

Author: Bruno Sgarbi

src/api/controllers/instance.controller.ts

@@ -458,15 +458,18 @@ export class InstanceController {
       if (instance.state === 'connecting' || instance.state === 'open') {
         try {
           await this.logout({ instanceName });
-        } catch (logoutError) {
-          // RIGARR PATCH: zombie instance cleanup.
-          // When a Baileys socket is dead but waInstances[name] still exists,
-          // logout() throws "Connection Closed". Without this catch, the
-          // remove.instance emit below never runs, leaving the zombie in memory
-          // forever (only fixable by restarting the entire container).
-          this.logger.warn(
-            `[ZOMBIE-CLEANUP] logout failed for "${instanceName}" (likely zombie socket): ${logoutError?.toString?.() || logoutError}. Proceeding with cleanup.`,
-          );
+        } catch (error) {
+          // logout can throw "Connection Closed" when the underlying Baileys
+          // socket is already dead but waInstances[name] still exists. We
+          // must continue to the remove.instance emit below — that is the
+          // only path that purges the in-memory entry and runs cleaningUp().
+          // Without this catch, the stale entry persists until the entire
+          // process restarts.
+          this.logger.warn({
+            message: 'logout failed during deleteInstance — proceeding with cleanup',
+            instanceName,
+            error,
+          });
         }
       }