`swarm.forge` (what the forge is to every hive: ports, domain, public and
root URLs, OIDC client id and callback) moves to
nix/host-modules/hive-forge/service.nix, together with the rename of the
old `services.hyperhive.forge` tree and the removed `swarm.forge.sso.enable`,
both of which name `swarm.forge` paths. Everything else -- the
`deploy.forgejo` options, the whole `config` block including
`containers.hive-forge`, and the helpers only they read -- stays in
nix/host-modules/hive-forge/default.nix, which now imports ./service.nix.
Importing it from the directory's own default.nix, as hive-c0re/ and
hive-gateway/ do with their option files, keeps the flake's standalone
`nixosModules.hive-forge` export whole.
Both halves read `cfg`, `gatewayCfg`, `swarmDomain` and `deployCfg`. They
are option reads, so each file binds them from `config`. `ssoSourceName`,
`defaultRootUrl` and `effectiveRootUrl` are not options and both halves
need them (the service half builds `sso.redirectUri` from them, the deploy
half registers the login source and sets ROOT_URL), so they are duplicated,
with a note at each copy. `ssoRedirectUri` is read only by the service
half and moves.
`swarm.forge.publicUrl` and `swarm.forge.sso.redirectUri` default from
`deploy.forgejo.behindGateway`; both move as they are.
A pure move: option paths, option definitions and config are unchanged
apart from comments: the two on either side of the cut, the
`ssoRedirectUri` comment and the duplication notes, and the rename
precedent in ./deploy.nix, which now names ./hive-forge/service.nix.
Refs #3742