Generate all UTF-8 locales, allow locale override via env vars

Users can set LANG, LANGUAGE, LC_ALL in .env to override the default
en_US.UTF-8 locale (e.g. sv_SE.UTF-8 for Swedish).

.env.example

@@ -31,6 +31,11 @@ WORKSPACE_PATH=~/projects
 # Path to SSH keys on host
 SSH_KEY_PATH=~/.ssh
 
+# ── Locale (defaults to en_US.UTF-8) ─────────────────────────────────
+# LANG=sv_SE.UTF-8
+# LANGUAGE=sv_SE:sv
+# LC_ALL=sv_SE.UTF-8
+
 # ── oh-my-opencode-slim (multi-agent orchestration) ──────────────────
 # Requires image built with INSTALL_OMOS=true
 # ENABLE_OMOS=false