Split InfoServ into one file per command

POST/DEL/LIST each move to their own file (each still parameterised by
bulletin kind, so OPOST/ODEL/OLIST route to the same handler); the kind
constants stay in lib.rs beside the dispatcher. No behaviour change.

modules/infoserv/src/post.rs

@@ -0,0 +1,18 @@
+use fedserv_api::{Priv, Sender, ServiceCtx, Store};
+
+// POST/OPOST <message>: add a bulletin (public or oper). Admin only.
+pub fn handle(me: &str, from: &Sender, kind: &str, rest: &[&str], ctx: &mut ServiceCtx, db: &mut dyn Store) {
+    if !from.privs.has(Priv::Admin) {
+        ctx.notice(me, from.uid, "Access denied — posting bulletins is for services operators.");
+        return;
+    }
+    let message = rest.join(" ");
+    if message.trim().is_empty() {
+        ctx.notice(me, from.uid, format!("Syntax: {} <message>", if kind == super::OPER { "OPOST" } else { "POST" }));
+        return;
+    }
+    let setter = from.account.unwrap_or(from.nick);
+    db.news_add(kind, &message, setter);
+    let which = if kind == super::OPER { "oper" } else { "public" };
+    ctx.notice(me, from.uid, format!("Added a \x02{which}\x02 bulletin."));
+}