docs: strengthen public security signals

.github/pull_request_template.md

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+## Summary
+
+- Describe the change.
+
+## Safety Review
+
+- Does this change affect cleanup, uninstall, optimize, installer, remove, analyze delete, update, or install behavior?
+- Does this change affect path validation, protected directories, symlink handling, sudo boundaries, or release/install integrity?
+- If yes, describe the new boundary or risk change clearly.
+
+## Tests
+
+- List the automated tests you ran.
+- List any manual checks for high-risk paths or destructive flows.
+
+## Safety-related changes
+
+- None.