new `services.hive-forge.enable` (off by default) wraps
`services.forgejo` with hyperhive-friendly defaults: sqlite (no
extra db service), built-in ssh on 2222 so it doesn't fight the
host's openssh, http on 3000 (outside hyperhive's 7000/8000/8100-8999
ranges), registration off (operator seeds agent users), private
repos by default. exported as `nixosModules.hive-forge` — operator
imports it on the host alongside hive-c0re. container-side wiring
(MCP tools or a bind-mounted token) is deferred; containers already
share the host netns so they can reach http://localhost:3000 today.
