Second split under docs/swarm/, following the shape docs/turn-loop/ and
docs/web-ui/ already use.
The README keeps the `## Swarm CA` heading rather than deleting it: an
existing cross-reference targets that anchor, and a heading is the
cheapest thing to preserve. It now carries the one-paragraph summary and
a pointer, so a reader who lands on the anchor still arrives somewhere
that answers the question.
The CA page also absorbs three things that were true but undocumented —
why the trust bundle rather than the bare intermediate (openssl will not
terminate a chain at a non-self-signed anchor without -partial_chain),
that autoConfigure derives from enableAllLocalDefaults, and that the
name constraint excludes both IP families because a permitted-DNS-only
constraint says nothing about IP SANs.
