chore: anonymize internal URLs for public release

Replace git.wxs.ro with forgejo.example.com in tests and docs.
Add public repo guidelines to CLAUDE.md.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -1,5 +1,13 @@
 # CLAUDE.md
 
+## Public Repository
+
+This repo is open-source and synced to Codeberg. When making changes:
+
+- **Never commit sensitive data** — no internal URLs, tokens, credentials, private infrastructure details, or instance-specific configuration in `src/`, `action.yml`, `base-action/`, or `docs/`. The `.forgejo/workflows/` directory is the only place with instance-specific config (runner labels, bot IDs, internal URLs) and that's fine — users write their own workflows.
+- **Keep Forgejo support generic** — all Forgejo code must work for any Forgejo instance, not just ours. Don't hardcode assumptions about our setup. Use action inputs and environment variables for instance-specific values.
+- **Use generic URLs in tests** — test fixtures use `forgejo.example.com` as the sample Forgejo URL. Never use real instance URLs in `src/` or `test/` code.
+
 ## Commands
 
 ```bash