fix: provisioning race condition and noisy ClickHouse logs

Defer provisionAsync() until after the transaction commits using
TransactionSynchronization.afterCommit(). Previously the @Async thread
raced the @Transactional commit — findById returned null because the
tenant INSERT wasn't visible yet.

Downgrade ClickHouse UNKNOWN_TABLE errors to DEBUG level in
InfrastructureService. These are expected on fresh installs before any
cameleer-server has created the tables.

Make the onboarding slug field read-only (derived from org name).

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

ui/src/pages/OnboardingPage.tsx

@@ -1,4 +1,4 @@
-import { useState, useEffect } from 'react';
+import { useState } from 'react';
 import { Card, Input, Button, FormField, Alert } from '@cameleer/design-system';
 import cameleerLogo from '@cameleer/design-system/assets/cameleer-logo.svg';
 import { api } from '../api/client';
@@ -14,16 +14,10 @@ interface TenantResponse {
 
 export function OnboardingPage() {
   const [name, setName] = useState('');
-  const [slug, setSlug] = useState('');
-  const [slugTouched, setSlugTouched] = useState(false);
   const [loading, setLoading] = useState(false);
   const [error, setError] = useState<string | null>(null);
 
-  useEffect(() => {
-    if (!slugTouched) {
-      setSlug(toSlug(name));
-    }
-  }, [name, slugTouched]);
+  const slug = toSlug(name);
 
   async function handleSubmit(e: React.FormEvent) {
     e.preventDefault();
@@ -78,10 +72,8 @@ export function OnboardingPage() {
                 <Input
                   id="onboard-slug"
                   value={slug}
-                  onChange={(e) => { setSlugTouched(true); setSlug(e.target.value); }}
                   placeholder="acme-corp"
-                  disabled={loading}
-                  required
+                  readOnly
                 />
               </FormField>