docs: update all documentation for email connector UI migration

- CLAUDE.md: add EmailConnectorService/Controller to vendor package
- .env.example: replace SMTP vars with note about runtime UI config
- docker/CLAUDE.md: update sign-in UI and bootstrap descriptions
- ui/CLAUDE.md: add EmailConfigPage, update sidebar and registration notes
- ui/sign-in/Dockerfile: update connector install comment
- installer: update README, .env.example (submodule)

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

ui/sign-in/Dockerfile

@@ -15,7 +15,7 @@ FROM ghcr.io/logto-io/logto:latest
 # Install bootstrap dependencies (curl, jq for API calls; postgresql16-client for DB reads)
 RUN apk add --no-cache curl jq postgresql16-client
 
-# Install all official Logto connectors (ensures SMTP email is available for self-hosted)
+# Install all official Logto connectors (email, SMS, social — configured at runtime via vendor UI)
 RUN cd /etc/logto/packages/core && npm run cli connector add -- --official 2>/dev/null || true
 
 # Custom sign-in UI