feat(tenant): welcome email, admin email display, async delete fix

- Send branded welcome email to tenant admin after provisioning completes
  (includes username and dashboard URL)
- Store admin_email on tenant entity (V004 migration)
- Show admin email in vendor tenant list table and detail page
- Fix ClickHouse cleanup: skip materialized views (can't ALTER DELETE on MVs)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/pages/vendor/TenantDetailPage.tsx

@@ -400,6 +400,12 @@ export function TenantDetailPage() {
               <span className={styles.kvLabel}>Slug</span>
               <span className={styles.kvValueMono}>{tenant.slug}</span>
             </div>
+            {tenant.adminEmail && (
+              <div className={styles.kvRow}>
+                <span className={styles.kvLabel}>Admin</span>
+                <span className={styles.kvValue}>{tenant.adminEmail}</span>
+              </div>
+            )}
             <div className={styles.kvRow}>
               <span className={styles.kvLabel}>Created</span>
               <span className={styles.kvValue}>{new Date(tenant.createdAt).toLocaleDateString()}</span>

ui/src/pages/vendor/VendorTenantsPage.tsx

@@ -41,6 +41,13 @@ const columns: Column<VendorTenantSummary>[] = [
       <span style={{ fontFamily: 'monospace', fontSize: '0.875rem' }}>{row.slug}</span>
     ),
   },
+  {
+    key: 'adminEmail',
+    header: 'Admin',
+    render: (_v, row) => (
+      <span style={{ fontSize: '0.875rem' }}>{row.adminEmail ?? '—'}</span>
+    ),
+  },
   {
     key: 'tier',
     header: 'Tier',

ui/src/types/api.ts

@@ -4,6 +4,7 @@ export interface TenantResponse {
   slug: string;
   tier: string;
   status: string;
+  adminEmail: string | null;
   serverEndpoint: string | null;
   provisionError: string | null;
   createdAt: string;
@@ -75,6 +76,7 @@ export interface VendorTenantSummary {
   slug: string;
   tier: string;
   status: string;
+  adminEmail: string | null;
   serverState: string;
   licenseExpiry: string | null;
   provisionError: string | null;