fix: member status visibility, team creation improvements, join approval flow

- Fix other members' status not visible due to users collection viewRule restriction
- Fix empty status treated as 'away' instead of 'idle' in membersByStatus
- Auto-set creator to 'in_team' status when creating team session
- Filter current user from idle members invite list
- Fix group store isGroupOwner using pb.authStore instead of localStorage
- Add nginx no-cache headers for index.html
- Add join_requests collection migration and join approval flow
- Update groups collection rules and add requireApproval field
- Add Memory types for Phase 2 planning

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/views/GroupView.vue

@@ -34,8 +34,9 @@ const membersByStatus = computed(() => {
     away: []
   }
   for (const m of members.value) {
-    if (groups[m.status]) {
-      groups[m.status].push(m)
+    const s = m.status || 'idle'
+    if (groups[s]) {
+      groups[s].push(m)
     } else {
       groups.away.push(m)
     }