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/cancel.rs

@@ -0,0 +1,14 @@
+use fedserv_api::{Sender, ServiceCtx, Store};
+
+// CANCEL: withdraw your own newest open ticket.
+pub fn handle(me: &str, from: &Sender, ctx: &mut ServiceCtx, db: &mut dyn Store) {
+    let who = from.account.unwrap_or(from.nick);
+    let mine = db.help_tickets(true).into_iter().find(|t| t.requester.eq_ignore_ascii_case(who));
+    match mine {
+        Some(t) => {
+            db.help_close(t.id);
+            ctx.notice(me, from.uid, format!("Your request \x02#{}\x02 has been cancelled.", t.id));
+        }
+        None => ctx.notice(me, from.uid, "You have no open request to cancel."),
+    }
+}