Support multiple allowed users for write access

MAPTOOL_ALLOWED_GITEA_USER now accepts a comma-separated list of
Gitea usernames instead of just one, for when more than one person
needs upload/delete/move access.

docs/deployment.adoc

@@ -95,12 +95,17 @@ it every push would silently log everyone out every time `main`
 changes) — generate it once (`openssl rand -hex 32`) and store that
 same value as the secret from then on, don't regenerate per-deploy.
 
-Register the OAuth2 application on the Gitea side (as the
-`MAPTOOL_ALLOWED_GITEA_USER` account): *Settings → Applications →
-Manage OAuth2 Applications → Create a new OAuth2 Application*, with
-redirect URI `https://map.priesol.net/auth/callback`. That gives you
-the client id/secret to store as the two `GITEA_OAUTH_*` secrets
-above.
+Register the OAuth2 application once, under any one Gitea account
+(doesn't need to be an allowed user itself — any Gitea account can
+authenticate through it, `MAPTOOL_ALLOWED_GITEA_USER` is what actually
+decides who gets write access): *Settings → Applications → Manage
+OAuth2 Applications → Create a new OAuth2 Application*, with redirect
+URI `https://map.priesol.net/auth/callback`. That gives you the client
+id/secret to store as the two `OAUTH_CLIENT_*` secrets above.
+
+`MAPTOOL_ALLOWED_GITEA_USER` itself is a comma-separated list of Gitea
+usernames, e.g. `randy,friend1,friend2` — not their emails, the
+`login` field from Gitea's `/api/v1/user`.
 
 == CI deploy job