Initial package for pnpr 0.1.0-alpha.5

Native binary taken from the @pnpm/pnpr.linux-{x64,arm64} npm platform
packages; systemd service with dynamic sysusers pnpr user. Storage in
/var/lib/pnpr, disposable proxy cache split into /var/cache/pnpr via
--cache. Default config proxies registry.npmjs.org; listen address and
extra flags via /etc/pnpr/pnpr.env.

pnpr.env

@@ -0,0 +1,13 @@
+# Environment for pnpr.service. Edit and restart:
+#   systemctl restart pnpr.service
+
+# Listen address. Loopback-only by default. To serve CI runner
+# containers, bind a reachable address (e.g. 0.0.0.0:7677 or the podman
+# bridge gateway) — see the addressing note in /etc/pnpr/pnpr.yaml.
+PNPR_LISTEN=127.0.0.1:7677
+
+# Extra pnpr flags (see pnpr --help). When PNPR_LISTEN is not loopback,
+# set --public-url to the URL clients use, or dist.tarball URLs in
+# served packuments are rewritten against the raw listen address:
+#   PNPR_OPTS=--public-url http://host.containers.internal:7677
+PNPR_OPTS=