fix(authority): skip members with incomplete data instead of panicking

[eejd]

Problem

ZTRecord::new() panics via .expect() in three places when a network member has incomplete data:

• node_id missing → expect("Node ID for member does not exist")
• config missing → expect("Member config does not exist")
• an ip_assignment that doesn't parse → IpAddr::from_str(s).expect("Could not parse IP address")

A single such member is enough to abort the whole configure_members() pass. The most common trigger in practice is an authorized member with no IPv4 assignment (e.g. an iOS/cellular client that has joined but not been assigned a managed IP). Because find_members() runs on a refresh loop and the process is normally run under a supervisor that restarts it on exit (launchd KeepAlive, systemd Restart=, Docker restart:), the panic becomes a crash loop that takes DNS down for the entire network until the offending member is given an IP or deauthorized.

Fix

Make ZTRecord::new() total:

• return an Err (the caller logs a warning and continues to the next member) when node_id is missing;
• treat a missing config as "no IP assignments";
• filter_map IP parsing so an unparseable address is dropped instead of fatal.

This mirrors the defensive filter_map already used a few lines up in configure_members() for the reverse-PTR path, so the two code paths now handle malformed member data consistently. A member with no usable IPs simply gets a hostname record with no A/AAAA (which match_or_insert already handles), instead of crashing the server.

No behavior change for well-formed members.

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