feat: member portal Sprint 7 — Circles (interest/affinity sub-groups)

- Circle + CircleMembership models + migration (CircleRole: MEMBER/LEAD, public/invite-only)
- CirclesModule: admin CRUD + member list; unique circle name per tenant
- Member endpoints in MyController: GET /my/circles, POST /my/circles/:id/join|leave
- listForMember returns public circles + private ones the member belongs to, with isMember/myRole/memberCount
- join() enforces invite-only; leave() removes membership
- /my/circles page: "My circles" + "Discover" split, join/leave button, LEAD + Private badges
- Member + admin BFF routes; Circles nav item
- Register CirclesModule; add CIRCLE_CREATED/DELETED audit actions

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/api/prisma/schema.prisma

@@ -94,6 +94,7 @@ model Tenant {
   threads        Thread[]
   sevaOpportunities  SevaOpportunity[]
   gamificationEvents GamificationEvent[]
+  circles            Circle[]
 }
 
 enum AdminRole {
@@ -420,6 +421,7 @@ model TowerUser {
   rsvps    EventRsvp[]
   sevaEntries        SevaEntry[]
   gamificationEvents GamificationEvent[]
+  circleMemberships  CircleMembership[]
 
   @@unique([tenantId, phoneHash])
   @@index([phoneHash])
@@ -689,3 +691,42 @@ model GamificationEvent {
   // One award per (user, type, ref) — prevents double-awarding the same source.
   @@unique([userId, type, refId])
 }
+
+// ============================================================================
+// Circles (interest / affinity sub-groups within a chapter)
+// ============================================================================
+
+enum CircleRole {
+  MEMBER
+  LEAD
+}
+
+model Circle {
+  id          String   @id @default(cuid())
+  tenantId    String
+  tenant      Tenant   @relation(fields: [tenantId], references: [id])
+  name        String
+  description String?
+  isPublic    Boolean  @default(true)
+  createdBy   String
+  createdAt   DateTime @default(now())
+  updatedAt   DateTime @updatedAt
+
+  memberships CircleMembership[]
+
+  @@unique([tenantId, name])
+  @@index([tenantId, isPublic])
+}
+
+model CircleMembership {
+  id        String     @id @default(cuid())
+  circleId  String
+  circle    Circle     @relation(fields: [circleId], references: [id], onDelete: Cascade)
+  userId    String
+  user      TowerUser  @relation(fields: [userId], references: [id])
+  role      CircleRole @default(MEMBER)
+  createdAt DateTime   @default(now())
+
+  @@unique([circleId, userId])
+  @@index([userId])
+}