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/glue-bao-tls.nix

@@ -261,6 +261,14 @@ in
         # is a swarm singleton, so elsewhere this is the file an operator copies.
         [ -s ${pkiDir}/nats-auth.pem ] || ${signLeaf} ${pkiDir} nats-auth \
           ${lib.escapeShellArg deployCfg.bao.natsAuthCommonName} "" clientAuth
+
+        # This hive's gateway-leaf identity, which opens
+        # `pki/issue/<hiveLeafPkiRolePrefix>-<hive>` and nothing else. Its
+        # subject carries this hive's name, like the matrix-token and
+        # queue-agent leaves above, because ./swarm-bao.nix writes one role per
+        # hive. Hives on other hosts are issued theirs out of band.
+        [ -s ${pkiDir}/hive-leaf.pem ] || ${signLeaf} ${pkiDir} hive-leaf \
+          ${lib.escapeShellArg "${deployCfg.bao.hiveLeafCommonNamePrefix}-${clientCn}"} "" clientAuth
       '';
     };
   };