docs(containers): add Shell In A Box host service

Add shellinabox web-based terminal emulator running on port 4200,
accessible via https://shell.schweitz.net through NPM reverse proxy.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

CONTAINERS.md

@@ -1,7 +1,7 @@
 # Container Reference - tower-of-joy Infrastructure
 
-> **Last Updated:** 2026-01-31
-> **Total Services:** 34 containers across 21 stacks  
+> **Last Updated:** 2026-02-12
+> **Total Services:** 35 containers across 21 stacks  
 > **System:** Intel i7-6700, RTX 2080 Ti (11GB VRAM), 64GB RAM, Zorin OS 16.3
 
 ---
@@ -40,6 +40,7 @@
 | **Paperless-ngx** | 8091 | https://documents.schweitz.net | Internet | No | 8 | ✅ Running |
 | **Penpot** | 9001 | https://penpot.schweitz.net | Internet (SSO) | No | 10 | ✅ Running |
 | **ClamAV** | 3310 | N/A (host service) | No | No | - | ✅ Running |
+| **Shell In A Box** | 4200 | https://shell.schweitz.net | Internet (host service) | No | - | ✅ Running |
 | **AdGuard Home** | 53, 3053 | http://dns.schweitz.internal | LAN (DNS) | No | - | ✅ Running |
 | **Tatlock UI** | 9999 | https://home.schweitz.net | Internet | No | - | ✅ Running |
 
@@ -51,6 +52,7 @@
 - **auth.schweitz.net** → Authentik SSO
 - **api.schweitz.net** → Core API
 - **code.schweitz.net** → Code-Server (host service)
+- **shell.schweitz.net** → Shell In A Box (host service)
 - **amp.schweitz.net** → AMP Game Server
 - **housekeeping.schweitz.net** → Home Assistant
 - **documents.schweitz.net** → Paperless-ngx
@@ -287,6 +289,31 @@ Code-Server provides a browser-based Visual Studio Code IDE running directly on
 
 ---
 
+### Shell In A Box
+
+Shell In A Box is a web-based terminal emulator that provides secure shell access to the host system through a browser, enabling command-line administration from any device without requiring an SSH client. It runs as a lightweight systemd service on the host, exposing a terminal interface via HTTP that is secured externally through Nginx Proxy Manager with SSL encryption. The service provides a quick way to access the host shell for system administration, troubleshooting, and maintenance tasks when a full IDE like Code-Server is not needed.
+
+| Property | Value |
+|----------|-------|
+| **Deployment Type** | Host-based systemd service (NOT containerized) |
+| **Binary Location** | `/usr/bin/shellinaboxd` |
+| **Service Name** | `shellinabox.service` |
+| **Access URL (LAN)** | http://192.168.86.149:4200 |
+| **Access URL (Public)** | https://shell.schweitz.net |
+| **External Access** | Yes (via NPM reverse proxy with SSL) |
+| **Port Binding** | 0.0.0.0:4200 (HTTP) |
+| **User/Group** | `shellinabox:shellinabox` (daemon), login as any system user |
+| **Restart Policy** | `on-failure` (systemd) |
+| **Config Location** | `/etc/default/shellinabox` |
+| **Resource Limits** | None (native host process) |
+| **GPU Required** | No |
+| **Dependencies** | NPM (reverse proxy) |
+| **Authentication** | System login (PAM), SSL via NPM |
+| **Typical Memory** | ~5-10MB |
+| **Features** | Web-based terminal, color themes, multiple sessions, copy/paste support |
+
+---
+
 ## Networking Layer
 
 ### Headscale
@@ -834,6 +861,7 @@ Gitea is a lightweight, self-hosted Git service providing repository hosting, is
 | **Redis Shared** | redis-shared:6379 | No (internal) | Shared cache/session store |
 | **NPM** | http://192.168.86.149:81 | Yes (admin) | Reverse proxy admin |
 | **Code-Server** | https://code.schweitz.net | Yes | Browser-based IDE |
+| **Shell In A Box** | https://shell.schweitz.net | Yes | Web-based terminal |
 | **Ollama** | http://192.168.86.149:11434 | No | ML model API |
 | **Headscale** | http://192.168.86.149:8085 | No | VPN control server |
 | **Open WebUI** | https://webui.schweitz.net | Yes (SSO) | LLM chat interface |