Add guest info screen with backups, backup now and network

Press i on a guest to see its backups and network. Backups from every
backup-capable storage are listed newest first, with the backup jobs
that cover the guest. The network part shows the netN settings
(bridge, VLAN, MAC, IPv4/IPv6 setting, firewall) and the addresses in
use.

Press b in the info screen to back the guest up now: snapshot mode and
zstd, like the scheduled job, to a storage you pick (the job's storage
is preselected). It asks for confirmation, marks the guest busy and
uses --wait.

Fixed after review and a read-only live check:
- prune-backups arrives as a JSON string; parsing it as a dict
  crashed the app.
- CT addresses come from ip-addresses. inet6 holds only the
  link-local address, so the global SLAAC address was missing.
- The info screen uses the guest's live status, and odd API data
  (null size, unknown address types) no longer kills the app.
- The test fake now copies guest dicts; a shared constant was being
  mutated across tests.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -20,6 +20,7 @@ uv run cv4pve-tui
 | `x` | stop - hard power-off (confirm) |
 | `r` | reboot (confirm) |
 | `e` | edit cores / memory / grow a disk (disk growth asks again; it cannot be undone) |
+| `i` | info: backups, backup job, network (config and runtime IPs); `b` there = backup now (snapshot, zstd, storage choice) |
 | `t` | shell in a running LXC container (`ssh -t root@<node> pct enter <vmid>`) |
 | `g` | refresh |
 | `c` | switch cv4pve-cli context (cluster) |