Change default PocketBase port to 8070

Set the default listen/host port to 8070 across both the rootless and
root stacks (previously 8080 rootless / 8081 root). Both internal and
external mappings derive from the same PB_PORT/PB_PORT_ROOT variables,
so a single change covers container and host.

Updated .env.example, both Dockerfiles (ENV/EXPOSE), both compose files
(env, port mapping, healthcheck), and both entrypoint fallbacks.

Note: both stacks now default to host port 8070, so they can no longer
run simultaneously without overriding PB_PORT_ROOT.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Dockerfile.rootless

@@ -45,8 +45,8 @@ VOLUME /pb/pb_data
 USER pb
 
 # default listen port; override at runtime with -e PB_PORT=...
-ENV PB_PORT=8080
-EXPOSE 8080
+ENV PB_PORT=8070
+EXPOSE 8070
 
 # shell form so ${PB_PORT} is expanded from the runtime environment
 HEALTHCHECK --interval=30s --timeout=5s --start-period=5s --retries=3 \