feat: self-service sign-up with email verification and onboarding

Complete sign-up pipeline: email registration via Logto Experience API,
SMTP email verification, and self-service trial tenant creation.

Layer 1 — Logto config:
- Bootstrap Phase 8b: SMTP email connector with branded HTML templates
- Bootstrap Phase 8c: enable SignInAndRegister (email+password sign-up)
- Dockerfile installs official Logto connectors (ensures SMTP available)
- SMTP env vars in docker-compose, installer templates, .env.example

Layer 2 — Experience API (ui/sign-in/experience-api.ts):
- Registration flow: initRegistration → sendVerificationCode → verifyCode
  → addProfile (password) → identifyUser → submit
- Sign-in auto-detects email vs username identifier

Layer 3 — Custom sign-in UI (ui/sign-in/SignInPage.tsx):
- Three-mode state machine: signIn / register / verifyCode
- Reads first_screen=register from URL query params
- Toggle links between sign-in and register views

Layer 4 — Post-registration onboarding:
- OnboardingService: reuses VendorTenantService.createAndProvision(),
  adds calling user to Logto org as owner, enforces one trial per user
- OnboardingController: POST /api/onboarding/tenant (authenticated only)
- OnboardingPage.tsx: org name + auto-slug form
- LandingRedirect: detects zero orgs → redirects to /onboarding
- RegisterPage.tsx: /platform/register initiates OIDC with firstScreen

Installers (install.sh + install.ps1):
- Both prompt for SMTP config in SaaS mode
- CLI args, env var capture, cameleer.conf persistence

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

ui/src/auth/RegisterPage.tsx

@@ -0,0 +1,32 @@
+import { useEffect, useRef } from 'react';
+import { useLogto } from '@logto/react';
+import { useNavigate } from 'react-router';
+import { Spinner } from '@cameleer/design-system';
+
+export function RegisterPage() {
+  const { signIn, isAuthenticated, isLoading } = useLogto();
+  const navigate = useNavigate();
+  const redirected = useRef(false);
+
+  useEffect(() => {
+    if (isAuthenticated) {
+      navigate('/', { replace: true });
+    }
+  }, [isAuthenticated, navigate]);
+
+  useEffect(() => {
+    if (!isLoading && !isAuthenticated && !redirected.current) {
+      redirected.current = true;
+      signIn({
+        redirectUri: `${window.location.origin}/platform/callback`,
+        firstScreen: 'register',
+      });
+    }
+  }, [isLoading, isAuthenticated, signIn]);
+
+  return (
+    <div style={{ display: 'flex', alignItems: 'center', justifyContent: 'center', minHeight: '100vh' }}>
+      <Spinner />
+    </div>
+  );
+}