chore: rebrand backone names, add lint gate + agent docs

- CI: build/validate use backone selftest + binary names, add lint.yml
- make-*.mk: emit/install backone binaries, drop zerotier-one paths
- doc/debian/ext.installfiles: backone manpages, service, init, te
- rule-compiler: npm test runs test.js; attic world planet files
- AGENTS.md repository guidelines, tools/lint.sh changed-lines gate
- gitignore: /backone-selftest, *.gcno, *.gcda

debian/backone.service

@@ -0,0 +1,12 @@
+[Unit]
+Description=BackOne
+After=network-online.target network.target
+Wants=network-online.target
+
+[Service]
+ExecStart=/usr/sbin/backone
+Restart=always
+KillMode=process
+
+[Install]
+WantedBy=multi-user.target