feat: add institutional membership tiers and correct member directory

Corrections per 2026-04 institutional review:
- MLFO reclassified as Global Family Office (was incorrectly labeled central bank)
- BIS Innovation Hub reclassified as Standards Body (does not hold observer seat)
- Added missing entities: ICCC, SAID, PANDA, Order of Hospitallers (XOM)
- Added BRICS founding + expanded member central banks (10 entries)

New institutional tier taxonomy (7 tiers):
  sovereign_central_bank, global_family_office, settlement_member,
  infrastructure_operator, oversight_judicial, delegated_authority,
  standards_body

Backend changes:
- New auth/membership.go: tier types, DefaultTrackForTier mapping,
  MembershipStore with DB queries for member directory
- New migration 0017: institutional_members + institutional_member_wallets
  tables with seed data for all corrected members
- Updated wallet_auth.go getUserTrack(): now resolves institutional
  membership (via wallet junction table) before defaulting to Track 1
- WalletAuthResponse now includes institutional_tier and institution_name
- New REST endpoints: GET /api/v1/membership/{tiers,members,members/:slug}
- Added TrackLabel() helper in featureflags

Frontend changes:
- Added InstitutionalTier type and label map to access.ts
- WalletAccessSession extended with institutionalTier/institutionName
- Navbar getAccessTier() now displays institutional tier label when present
- Session summary shows institution name

Co-Authored-By: Nakamoto, S <defi@defi-oracle.io>

frontend/src/components/common/Navbar.tsx

@@ -3,7 +3,7 @@
 import Link from 'next/link'
 import { usePathname, useRouter } from 'next/navigation'
 import { type ReactNode, useEffect, useId, useMemo, useRef, useState } from 'react'
-import { accessApi, type WalletAccessSession } from '@/services/api/access'
+import { accessApi, institutionalTierLabels, type WalletAccessSession } from '@/services/api/access'
 import BrandLockup from './BrandLockup'
 import HeaderCommandPalette, { type HeaderCommandItem } from './HeaderCommandPalette'
 import { useUiMode } from './UiModeContext'
@@ -310,6 +310,9 @@ function SearchControl({
 }
 
 function getAccessTier(walletSession: WalletAccessSession) {
+  if (walletSession.institutionalTier) {
+    return institutionalTierLabels[walletSession.institutionalTier] ?? walletSession.institutionalTier
+  }
   const permissions = walletSession.permissions || []
   if (permissions.some((permission) => permission.startsWith('operator.'))) {
     return 'Operator Tier'
@@ -326,10 +329,11 @@ function getAccessTier(walletSession: WalletAccessSession) {
 function getSessionSummary(walletSession: WalletAccessSession) {
   const permissionCount = walletSession.permissions?.length || 0
   const tierLabel = getAccessTier(walletSession)
+  const institutionSuffix = walletSession.institutionName ? ` (${walletSession.institutionName})` : ''
   if (permissionCount > 0) {
-    return `${tierLabel} · ${permissionCount} permission${permissionCount === 1 ? '' : 's'}`
+    return `${tierLabel}${institutionSuffix} · ${permissionCount} permission${permissionCount === 1 ? '' : 's'}`
   }
-  return `${tierLabel} · Explorer access active`
+  return `${tierLabel}${institutionSuffix} · Explorer access active`
 }
 
 function UiModeToggle({ mobile = false }: { mobile?: boolean }) {