tweak forgejo service configuration a bit making it nicer

- Enable Git LFS support, since it's nice to have.
- Enable offline mode to avoid relying on CDNs (and to not use
  Gravatar).
- Disable internal sign-in, since OIDC is used and forced for
  registrations anyway.
- Enable notification mails for repo activity.
- Put setting for default repo units into "repository" category as the
  "repo" category doesn't exist.

config/hosts/forgejo/forgejo.nix

@@ -4,6 +4,7 @@
     enable = true;
     package = pkgs.forgejo;
     database.type = "postgres";
+    lfs.enable = true;
 
     settings = {
       DEFAULT = {
@@ -17,6 +18,7 @@
         ROOT_URL = "https://git.nekover.se/";
         # LOCAL_ROOT_URL is apparently what Forgejo uses to access itself.
         # Doesn't need to be set.
+        OFFLINE_MODE = true;
       };
       admin = {
         DISABLE_REGULAR_ORG_CREATION = false;
@@ -31,14 +33,14 @@
       };
       service = {
         ALLOW_ONLY_EXTERNAL_REGISTRATION = true;
+        ENABLE_INTERNAL_SIGNIN = false;
         DEFAULT_USER_VISIBILITY = "limited";
         DEFAULT_KEEP_EMAIL_PRIVATE = true;
         ENABLE_BASIC_AUTHENTICATION = false;
-      };
+        ENABLE_NOTIFY_MAIL = true;
-      repo = {
-        DEFAULT_REPO_UNITS = "repo.code,repo.issues,repo.pulls";
       };
       repository = {
+        DEFAULT_REPO_UNITS = "repo.code,repo.issues,repo.pulls";
         ENABLE_PUSH_CREATE_USER = true;
         ENABLE_PUSH_CREATE_ORG = true;
       };