refactor(3202): the forge declares its own vhost and dns name

Moves `forgeVhost` out of the gateway's vhosts.nix and the forge's
`address=` rule out of dnsmasq.nix, into nix/host-modules/hive-forge —
the module that already owns everything else about the forge.

The gateway keeps what is gateway knowledge (the listen set, which
issuer covers a name, the header block) and loses the last reason it
had to read `swarm.forge` at all: `forgeCfg` is gone from both files
and from the module's `let`.

Both halves stay gated on `behindGateway` — with it off the operator
fronts forgejo themselves, so this hive must neither claim the vhost nor
answer DNS for the name.

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

@@ -25,7 +25,6 @@ let
   autheliaCfg = config.services.hyperhive.swarm.authelia;
   uiCfg = config.services.hyperhive.swarm.ui;
   controllerCfg = config.services.hyperhive.swarm.controller;
-  forgeCfg = config.services.hyperhive.swarm.forge;
   networkCfg = config.services.hyperhive.network;
 
   # Dashboard SPA dist, static-served by nginx.
@@ -87,7 +86,6 @@ let
     inherit
       lib
       cfg
-      forgeCfg
       matrixCfg
       autheliaCfg
       uiCfg
@@ -374,7 +372,6 @@ in
         lib
         cfg
         networkCfg
-        forgeCfg
         matrixCfg
         autheliaCfg
         uiCfg