fix(render+roles): batch smooth shading + step timings + global_admin role support

Render pipeline:
- Replace per-object _apply_smooth() loop with _apply_smooth_batch(): selects
  all 175 parts, calls shade_smooth_by_angle() ONCE in C → reduces 16s to ~0.2s
- Remove 175 per-part "assigned material to part" log lines (replace with summary)
- Add TIMING_SUMMARY log line at end of every render showing all step durations
- _lap() helper records split times for: template_load, glb_import, rotation,
  smooth_shading, material_assign, pre_render_setup, gpu_render

Frontend role checks:
- Add global_admin + tenant_admin to User role type in auth store
- Add isAdmin() and isPrivileged() helper functions
- Fix Admin.tsx, Layout.tsx, Notifications.tsx, OrderDetail.tsx, ProductDetail.tsx,
  CostOverviewWidget.tsx — all were checking role === 'admin' but JWT now has
  role === 'global_admin' after migration 049 (admin → global_admin backfill)
- This caused Admin page to render completely empty

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

frontend/src/pages/Admin.tsx

@@ -10,7 +10,7 @@ import TemplateEditor from '../components/admin/TemplateEditor'
 import PricingTierTable from '../components/admin/PricingTierTable'
 import OutputTypeTable from '../components/admin/OutputTypeTable'
 import RenderTemplateTable from '../components/admin/RenderTemplateTable'
-import { useAuthStore } from '../store/auth'
+import { useAuthStore, isAdmin as checkIsAdmin } from '../store/auth'
 import { listPricingTiers } from '../api/pricing'
 import { listOutputTypes } from '../api/outputTypes'
 import {
@@ -26,7 +26,7 @@ import type { GPUProbeResult } from '../api/worker'
 export default function AdminPage() {
   const qc = useQueryClient()
   const user = useAuthStore((s) => s.user)
-  const isAdmin = user?.role === 'admin'
+  const isAdmin = checkIsAdmin(user)
   const [showNewUser, setShowNewUser] = useState(false)
   const [newUser, setNewUser] = useState({ email: '', password: '', full_name: '', role: 'client' })
   const [editingTemplateId, setEditingTemplateId] = useState<string | null>(null)
@@ -335,7 +335,7 @@ export default function AdminPage() {
                 <p className="text-sm font-medium text-content">{user.full_name}</p>
                 <p className="text-xs text-content-muted">{user.email}</p>
               </div>
-              <span className={`badge mr-4 ${user.role === 'admin' ? 'badge-green' : 'badge-gray'}`}>
+              <span className={`badge mr-4 ${checkIsAdmin(user) ? 'badge-green' : 'badge-gray'}`}>
                 {user.role}
               </span>
               <span className={`badge mr-4 ${user.is_active ? 'badge-green' : 'badge-red'}`}>