feat: member portal Sprint 6 — Seva + multi-signal gamification

- SevaOpportunity + SevaEntry + GamificationEvent models + migration
- GamificationService: multi-signal point table (helpful answer +10, seva +20,
  event +5, FAQ +15, welcome +3, profile +5, business +5), idempotent award via
  unique(userId,type,refId), lifetime + time-decayed "recent" score, leaderboard
- SevaModule: admin CRUD + mark-entry-complete (awards SEVA_COMPLETED points)
- Member endpoints in MyController: GET /my/seva, POST /my/seva/:id/signup|cancel
- PROFILE_COMPLETED auto-awarded on profile update (name+hometown+interest)
- /my/seva page: points hero with per-type breakdown, open opportunities w/ signup,
  leaderboard (respects directoryVisible), my seva history
- Member + admin BFF routes; Seva & Points nav item
- Register GamificationModule + SevaModule; add SEVA_* audit actions

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

apps/web/app/my/layout.tsx

@@ -6,6 +6,7 @@ const NAV = [
   { href: '/my', label: 'Dashboard' },
   { href: '/my/digest', label: 'Digest' },
   { href: '/my/events', label: 'Events' },
+  { href: '/my/seva', label: 'Seva & Points' },
   { href: '/my/groups', label: 'My Groups' },
   { href: '/my/settings', label: 'Settings' },
 ];