fix(systemd): set explicit SyslogIdentifier on hyperhive-declared units

Follow-up to the harness fix: any unit whose ExecStart is a generated
wrapper (a NixOS `script =` block or a writeShellScript) gets its journal
SyslogIdentifier derived from the wrapper's store-path basename — an
opaque, unstable name. Pin an explicit stable identifier on every unit
hyperhive declares.

script/wrapper units (leaked store paths): forgejo-gpg-init,
hive-gateway-self-signed-cert, hive-tls-ca, hive-ci-prefetch,
hyperhive-isolated-dns, tea-login, forge-avatar-sync,
matrix-avatar-sync, hive-dashboard-links.

direct-binary units (basename already sane; explicit for tidiness +
future-proofing): hive-c0re, hive-priv, hive-matrix-daemon,
hive-bash-daemon, weston.

Only changes the displayed line identifier; journalctl -u <unit>
filtering (keys on _SYSTEMD_UNIT) is unaffected.

nix/modules/hive-c0re.nix

@@ -973,6 +973,7 @@ in
           };
       serviceConfig = {
         ExecStart = "${cfg.package}/bin/hive-c0re --socket /run/hyperhive/host.sock serve --config ${serveConfig}";
+        SyslogIdentifier = "hive-c0re";
         # Migrate hive-c0re's *own* state to the service user after an
         # upgrade from a root-run install (systemd's StateDirectory only
         # chowns the top-level dir, not pre-existing files inside it). The
@@ -1109,6 +1110,7 @@ in
       };
       serviceConfig = {
         ExecStart = "${cfg.package}/bin/hive-priv";
+        SyslogIdentifier = "hive-priv";
         Type = "simple";
         User = "root";
         PrivateTmp = true;