Add optional oh-my-opencode-slim multi-agent orchestration support

Integrate oh-my-opencode-slim as an opt-in feature via INSTALL_OMOS build arg.
A single build arg installs Bun, tmux, and the plugin; runtime activation is
controlled by ENABLE_OMOS and related env vars in the entrypoint.

.env.example

@@ -30,3 +30,10 @@ WORKSPACE_PATH=~/projects
 
 # Path to SSH keys on host
 SSH_KEY_PATH=~/.ssh
+
+# ── oh-my-opencode-slim (multi-agent orchestration) ──────────────────
+# Requires image built with INSTALL_OMOS=true
+# ENABLE_OMOS=false
+# OMOS_TMUX=false              # Enable tmux multiplexer integration
+# OMOS_SKILLS=true             # Install recommended skills (simplify, agent-browser, cartography)
+# OMOS_RESET=false             # Force regenerate oh-my-opencode-slim config on next start