Split HelpServ into one file per command

REQUEST/CANCEL/LIST/VIEW/TAKE/NEXT/CLOSE each move to their own file;
the oper guard and the shared claim helper stay in lib.rs beside the
dispatcher. No behaviour change.

modules/helpserv/src/next.rs

@@ -0,0 +1,12 @@
+use fedserv_api::{Sender, ServiceCtx, Store};
+
+// NEXT: claim the oldest unassigned ticket.
+pub fn handle(me: &str, from: &Sender, ctx: &mut ServiceCtx, db: &mut dyn Store) {
+    if !super::require_oper(me, from, ctx) {
+        return;
+    }
+    match db.help_next_open() {
+        Some(id) => super::take_id(me, from, id, ctx, db),
+        None => ctx.notice(me, from.uid, "No unassigned tickets are waiting."),
+    }
+}