* fix: S3 copying test Makefile syntax and add S3_ENDPOINT env support
* fix: add weed mini to stop-seaweedfs target
Ensure weed mini process is properly killed when stopping SeaweedFS,
matching the process started in start-seaweedfs target.
* Clean up PID file in stop-seaweedfs and clean targets
Address review feedback to ensure /tmp/weed-mini.pid is removed
for a clean state after tests.