Add CLAUDE.md: no user data in the repo

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013wi3ZQveYdjfcrEsyazq32

CLAUDE.md

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+# CLAUDE.md
+
+## No user data in the repo
+
+Never write anything specific to a person's kiosk, network or accounts into
+this repository - not in code, tests, fixtures, docs, comments, commit
+messages, branch names or pull request text.
+
+That includes:
+
+- WiFi network names (SSIDs), passwords, keys and tokens
+- MAC addresses, IP addresses, hostnames and interface names taken from a
+  real machine
+- usernames, email addresses, PINs and passwords
+- the URLs of someone's own sites or services
+- log output, screenshots or terminal output pasted in by a user
+
+When an example, test or fixture needs a value like these, use an obvious
+placeholder (`ExampleNet`, `192.0.2.10`, `aa:bb:cc:dd:ee:ff`, `wlan0`,
+`example.com`) instead of a real one. When debugging from output a user
+shares, keep it in the conversation or the scratchpad, not in a file in this
+repo, and leave it out of commit messages.