fix: improve robustness and security in database restore flows

- Add null checks for server instances in restore events to prevent errors
- Escape S3 credentials to prevent command injection vulnerabilities
- Fix file upload clearing custom location to prevent UI confusion
- Optimize isSafeTmpPath helper by avoiding redundant dirname calls
- Remove unnecessary --rm flag from long-running S3 restore container
- Prioritize uploaded files over custom location in import logic
- Add comprehensive unit tests for restore event null server handling

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

app/Events/S3RestoreJobFinished.php

@@ -49,7 +49,10 @@ class S3RestoreJobFinished
                 }
             }
 
-            instant_remote_process($commands, Server::find($serverId), throwError: false);
+            $server = Server::find($serverId);
+            if ($server) {
+                instant_remote_process($commands, $server, throwError: false);
+            }
         }
     }
 }