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>

.env.example

@@ -28,13 +28,8 @@ 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
+# SMTP / email connector configuration is managed at runtime via the vendor
+# admin UI (Email Connector page at /vendor/email). No SMTP env vars needed.
 
 # TLS (leave empty for self-signed)
 # NODE_TLS_REJECT=0  # Set to 1 when using real certificates