add charm IPv4/IPv6 compatibility reference; confirm IPv4 config intact ...

Operator request: a durable per-charm IPv4/IPv6 compatibility reference, and
confirmation the IPv4 config still exists for the revert.

docs/charm-ip-family-compatibility.md -- all 33 distinct bundle charms, built
from the repo's MEASURED research (prefer-ipv6 charm research 07-31; the
ceph/hacluster/mysql/OVN findings in CURRENT-STATE:2480-2503) with LP citations.
Charms the repo has not measured for v6 are marked NOT ASSESSED rather than
guessed. Frames the two independent v6 blockers: juju container addressing
(LP#1723240, charm-independent, blocks all API-charm v6 VIPs today) and the
per-charm defects (hacluster ip_version ipv4 LP#2111852 fix-committed-unreleased;
ceph-osd LP#2109798+2061836; mysql bare-URI; OVN encap IPv4-only).

IPv4 config CONFIRMED INTACT by measurement: the current VIP overlay is
dual-stack -- every vip line carries the v4 triple AND the v6 triple, and the v4
legs are live and accepted. Revert = drop the v6 legs from render/values and
re-render; also in git at the parent of a9e3258 and reconstructable from
lib-net.sh. The node-plane v6 work stays; only the container-VIP family reverts.

repo-lint 0 fail.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HvCyrwvYTTcDYnRErfMsNf