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>

.env.example

@@ -28,6 +28,14 @@ CLICKHOUSE_PASSWORD=change_me_in_production
 SAAS_ADMIN_USER=admin
 SAAS_ADMIN_PASS=change_me_in_production
 
+# SMTP (for email verification during registration)
+# Required for self-service sign-up. Without SMTP, only admin-created users can sign in.
+SMTP_HOST=
+SMTP_PORT=587
+SMTP_USER=
+SMTP_PASS=
+SMTP_FROM_EMAIL=noreply@cameleer.io
+
 # TLS (leave empty for self-signed)
 # NODE_TLS_REJECT=0  # Set to 1 when using real certificates
 # CERT_FILE=