feat(classes): per-session signups roster on /classes/manage (staff)

Reuses the existing SessionAttendance component (listSessionSignups,
classes.manage/instruct-gated) behind a per-session 'Signups' toggle on
the manage page, so managers can see who signed up + status + mark
attendance + complete without leaving the manage screen. Members still
see only spots-left (privacy posture unchanged).

app/(app)/classes/manage/classes-manage-client.tsx

@@ -17,6 +17,7 @@ import {
   deleteSession,
 } from '@/lib/actions'
 import { SESSION_STATUS_LABEL } from '@/lib/classes-logic'
+import { SessionAttendance } from '@/components/classes/session-attendance'
 
 type Cls = {
   id: string
@@ -77,6 +78,7 @@ export function ClassesManageClient({
   const [editDraft, setEditDraft] = useState(emptyClassDraft())
   const [sessForClass, setSessForClass] = useState<string | null>(null)
   const [sessDraft, setSessDraft] = useState(emptySessionDraft())
+  const [rosterFor, setRosterFor] = useState<string | null>(null)
   const [busy, setBusy] = useState(false)
 
   function certName(id: string | null) {
@@ -395,7 +397,8 @@ export function ClassesManageClient({
                     ) : (
                       <ul className="divide-y divide-border">
                         {cs.map(s => (
-                          <li key={s.id} className="py-2 flex items-center justify-between gap-3 flex-wrap">
+                          <li key={s.id} className="py-2">
+                            <div className="flex items-center justify-between gap-3 flex-wrap">
                               <div className="font-mono text-[11px] text-muted-foreground">
                                 {new Date(s.starts_at).toLocaleString()}
                                 {s.location ? ` · ${s.location}` : ''}
@@ -406,11 +409,26 @@ export function ClassesManageClient({
                                 </span>
                               </div>
                               <div className="flex items-center gap-1.5">
+                                <Button size="sm" variant="outline"
+                                  onClick={() => setRosterFor(rosterFor === s.id ? null : s.id)}>
+                                  {rosterFor === s.id ? 'Hide signups' : 'Signups'}
+                                </Button>
                                 {s.status === 'scheduled' && (
                                   <Button size="sm" variant="outline" onClick={() => onCancelSession(s)}>Cancel</Button>
                                 )}
                                 <Button size="sm" variant="outline" onClick={() => onDeleteSession(s)}>Delete</Button>
                               </div>
+                            </div>
+                            {rosterFor === s.id && (
+                              <SessionAttendance
+                                sessionId={s.id}
+                                sessionStatus={s.status}
+                                onCompleted={() => {
+                                  setSessions(prev => prev.map(x => (x.id === s.id ? { ...x, status: 'completed' } : x)))
+                                  setRosterFor(null)
+                                }}
+                              />
+                            )}
                           </li>
                         ))}
                       </ul>