docs: add PR hygiene check to CLAUDE.md and contributing guidelines

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -48,6 +48,18 @@ Four types of skills exist in NanoClaw. See [CONTRIBUTING.md](CONTRIBUTING.md) f
 
 Before creating a PR, adding a skill, or preparing any contribution, you MUST read [CONTRIBUTING.md](CONTRIBUTING.md). It covers accepted change types, the four skill types and their guidelines, SKILL.md format rules, PR requirements, and the pre-submission checklist (searching for existing PRs/issues, testing, description format).
 
+## PR Hygiene
+
+Before pushing or creating a PR, run these checks and show the output to the user for approval:
+
+```bash
+git diff upstream/main --name-only HEAD
+git diff upstream/main --stat HEAD
+git log upstream/main..HEAD --oneline
+```
+
+If any personal files appear (CLAUDE.md, .claude/, personal configs, group data), remove them before pushing. Do not push until the user confirms the diff is clean.
+
 ## Development
 
 Run commands directly—don't tell the user to run them.

CONTRIBUTING.md

@@ -123,7 +123,8 @@ Test your contribution on a fresh clone before submitting. For skills, run the s
 
 1. **Link related issues.** If your PR resolves an open issue, include `Closes #123` in the description so it's auto-closed on merge.
 2. **Test thoroughly.** Run the feature yourself. For skills, test on a fresh clone.
-3. **Check the right box** in the PR template. Labels are auto-applied based on your selection:
+3. **Check for personal files.** Before pushing, verify no personal files are in your diff (see PR Hygiene in CLAUDE.md).
+4. **Check the right box** in the PR template. Labels are auto-applied based on your selection:
 
 | Checkbox | Label |
 |----------|-------|