hive-tls: issue the gateway leaf from bao with a per-hive identity

Every hive gets its own store identity (CN
<deploy.bao.hiveLeafCommonNamePrefix>-<hive>) and its own role on the
existing pki mount (<deploy.bao.hiveLeafPkiRolePrefix>-<hive>), whose
allowed_domains is the hive's domain and *.<domain>. The policy grants
update on that one issue path. swarm-bao-hive-leaf-policy writes role,
policy and cert-auth role for every hive in swarm.hives; the store's host
mints its own hive's identity in glue-bao-tls.nix and a new glue file
points deploy.hive-controller.tls.baoHiveIdentity{Cert,Key}File at it.
Hives on other hosts place it by hand. swarm.nix reserves the composed CN.

hive-tls-ca no longer generates a hive CA or signs a leaf: caGenScript,
signLeafScript/signHiveLeaf and the adoption block are gone, ca-key.pem
is deleted where it exists, and the unit only assembles trust-bundle.pem.
The retired ca.pem/ca-previous.pem stay in the bundle so leaves they
signed keep verifying.

hive-tls-resign becomes the bao issuance: at boot, on deploy and from a
daily timer it re-issues when the leaf is missing, past half the role's
lifetime, missing a name, or not chained to the store's pki root. Nothing
orders the gateway after it, so a valid leaf on disk never waits on the
store; a failed renewal leaves the leaf in place. A missing identity
fails the unit naming both options, as does the root fetch on a hive
fronting no swarm name, which now presents this identity instead of the
reader cert.

caValidityDays and leafValidityDays are removed (both spellings), since
nothing reads them.

Refs #4588

nix/host-modules/hive-gateway/default.nix

@@ -286,7 +286,7 @@ in
         chmod 0755 ${tlsDir}
         # Copy the leaf in. `install` writes atomically with the
         # target mode; runs as root so the 0600 root:root key written
-        # by hive-tls-ca is readable. Key ends up root:nginx 0640 so
+        # by hive-tls-resign is readable. Key ends up root:nginx 0640 so
         # nginx-pre-start
         # (which runs `nginx -t` as the nginx user, not root) can
         # read it — a 0600 root:root key passes the master load but