Add pull request template

Author: thedavidweng

.github/PULL_REQUEST_TEMPLATE.md

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+## Summary
+
+Brief description of the changes.
+
+## Changes
+
+- 
+
+## Test plan
+
+- [ ] `go test ./... -race` passes
+- [ ] `go vet ./...` clean
+- [ ] `gofmt -l` empty
+- [ ] New/changed commands tested with `--json` output
+- [ ] Safety model respected (dry-run, confirm, read-only) *(if applicable)*
+
+## Related issues
+
+Closes #