feat(installer): add --registry, --registry-user, --registry-token

Both installers (bash + PS1) now support pulling images from a
custom Docker registry. Writes *_IMAGE env vars to .env so compose
templates use the configured registry. Runs docker login before
pull when credentials are provided. Persisted in cameleer.conf
for upgrades/reconfigure.

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

installer/CLAUDE.md

@@ -31,6 +31,14 @@ Env vars: `SMTP_HOST`, `SMTP_PORT` (default 587), `SMTP_USER`, `SMTP_PASS`, `SMT
 
 CLI args: `--smtp-host`, `--smtp-port`, `--smtp-user`, `--smtp-pass`, `--smtp-from-email` (bash) / `-SmtpHost`, `-SmtpPort`, `-SmtpUser`, `-SmtpPass`, `-SmtpFromEmail` (PS1). Persisted in `cameleer.conf` for upgrades/reconfigure.
 
+## Registry configuration
+
+Both installers support pulling images from a custom Docker registry via `--registry` (bash) / `-Registry` (PS1). Default: `gitea.siegeln.net/cameleer`.
+
+When a registry is configured, the installer writes `*_IMAGE` env vars to `.env` (e.g. `TRAEFIK_IMAGE`, `POSTGRES_IMAGE`, `CAMELEER_IMAGE`) which override the defaults baked into the compose templates. In SaaS mode, provisioning image refs (`CAMELEER_SAAS_PROVISIONING_*IMAGE`) are also set from the registry.
+
+For private registries, pass `--registry-user` / `--registry-token` (bash) or `-RegistryUser` / `-RegistryToken` (PS1). The installer runs `docker login` before pulling images. Credentials are persisted in `cameleer.conf` for upgrades/reconfigure.
+
 ## Env var naming convention
 
 - `CAMELEER_AGENT_*` — agent config (consumed by the Java agent)