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/sign-in/src/SignInPage.module.css

@@ -12,7 +12,7 @@
   padding: 32px;
 }
 
-.loginForm {
+.formContainer {
   display: flex;
   flex-direction: column;
   align-items: center;
@@ -53,6 +53,53 @@
   width: 100%;
 }
 
+.passwordWrapper {
+  position: relative;
+}
+
+.passwordToggle {
+  position: absolute;
+  right: 8px;
+  top: 50%;
+  transform: translateY(-50%);
+  background: none;
+  border: none;
+  cursor: pointer;
+  color: var(--text-muted);
+  padding: 4px;
+  display: flex;
+  align-items: center;
+}
+
 .submitButton {
   width: 100%;
 }
+
+.switchText {
+  text-align: center;
+  font-size: 13px;
+  color: var(--text-muted);
+  margin: 4px 0 0;
+}
+
+.switchLink {
+  background: none;
+  border: none;
+  cursor: pointer;
+  color: var(--text-link, #C6820E);
+  font-size: 13px;
+  padding: 0;
+  text-decoration: underline;
+}
+
+.switchLink:hover {
+  opacity: 0.8;
+}
+
+.verifyHint {
+  font-size: 14px;
+  color: var(--text-secondary, var(--text-muted));
+  margin: 0 0 4px;
+  text-align: center;
+  line-height: 1.5;
+}