[Docs] Correct self-hosting operator guidance

[roomote-community]

​Created by Roomote. View the task or mention @roomote for follow-up asks.

What changed

• correct self-hosted and homelab RAM guidance, require elevated installer and host CLI examples, and document the current service heap caps
• document the local Caddy tunnel port and automatic Brain startup
• align supported deployment environment variables, parser values, defaults, restart behavior, and process-owned sandbox configuration with the implementation

Why this change was made

The operator documentation had drifted from the installer, runtime schemas, process entrypoints, and local development startup behavior. These corrections prevent invalid commands and misleading deployment configuration.

Impact

Operators and contributors now receive accurate setup, resource, privilege, and environment-variable guidance. This is a documentation-only change with no runtime behavior change.

[roomote-community]

1 issue outstanding. See task

• apps/docs/environment-variables.mdx:231 incorrectly says R_BRAIN_MODEL needs an API restart; the gateway reads the override for each inference request.

_{Reviewed 736c975}

[roomote-community]

R_BRAIN_MODEL is read by mapBrainModelName for each Brain inference request, so its override takes effect without restarting the API service. The new restart instruction is incorrect and causes needless downtime; document that it applies immediately instead.